Where does this definition of humility come from, if not the Catechism of the Catholic Church?

Where does this definition of humility come from, if not the Catholic catechism?

The quote (“The virtue by which a Christian acknowledges that God is the author of all good"?“) which you are seeking through your clarification notice can be found in the Glossary of the Catechism of the Catholic Church.

The Catechism of the Catholic Church is simply a readable tool for the average Catholic to understand various concepts and truths about what the Church professes. As such, in a general sense, it does not delve too deep into the various subject sources that it contains.

It is thus understandable that if one desired to obtain further information on some subject one should explore what the Church teaches on it though the eyes of her great theologians, Doctors of the Church such as St. Thomas Aquinas, the Church Fathers and other valuable Catholic sources.

Thus for humility the Catechism of the Catholic Church states the following as you have pointed out:

2559 "Prayer is the raising of one's mind and heart to God or the requesting of good things from God." But when we pray, do we speak from the height of our pride and will, or "out of the depths" of a humble and contrite heart? He who humbles himself will be exalted; humility is the foundation of prayer, Only when we humbly acknowledge that "we do not know how to pray as we ought," are we ready to receive freely the gift of prayer. "Man is a beggar before God."

Being a readable Catechism, we must search elsewhere for more details about humility.

The Catholic Encyclopedia has this to say about humility:

The word humility signifies lowliness or submissiveness and it is derived from the Latin humilitas or, as St. Thomas says, from humus, i.e. the earth which is beneath us. As applied to persons and things it means that which is abject, ignoble, or of poor condition, as we ordinarily say, not worth much. Thus we say that a man is of humble birth or that a house is a humble dwelling. As restricted to persons, humility is understood also in the sense of afflictions or miseries, which may be inflicted by external agents, as when a man humiliates another by causing him pain or suffering. It is in this sense that others may bring about humiliations and subject us to them. Humility in a higher and ethical sense is that by which a man has a modest estimate of his own worth, and submits himself to others. According to this meaning no man can humiliate another, but only himself, and this he can do properly only when aided by Divine grace. We are treating here of humility in this sense, that is, of the virtue of humility.

The virtue of humility may be defined: "A quality by which a person considering his own defects has a lowly opinion of himself and willingly submits himself to God and to others for God's sake." St. Bernard defines it: "A virtue by which a man knowing himself as he truly is, abases himself." These definitions coincide with that given by St. Thomas: "The virtue of humility", he says, "Consists in keeping oneself within one's own bounds, not reaching out to things above one, but submitting to one's superior" (Summa Contra Gent., bk. IV, ch. lv, tr. Rickaby).

In conclusion, I would like to finish by stating the 12 degrees of humility as seen though the eyes of St. Benedict of Nursia:

The First Step of Humility: The fear of God

“The first step of humility, then, is that a man keeps the fear of God always before his eyes (Psalm 36:2) and to never forget what God has commanded of us. Bearing before our minds the notion that those who despise God in their sinfulness will burn in Hell on account of their lack of love and on their turning away from Him is how man is to understand and fear God’s judgment. Though we must just as well say that the fear of God is that reverence we are to have of offending God who is the very principle of life and existence for all things. To offend Him ought to offend us, and so we must keep sure to guard our vices of thought or hold our tongue. Hence in order to hold ourselves true to God we must have the humility to withhold our own will in every act, but instead look to God Who’s will we pray in the Our Father to be done on Earth as it is in Heaven. All of our desires, our thoughts, our willful actions must be on guard and willing to lovingly offer up our entire selves up to God for Him to lead us and guide us to keep His commandments. And so we must be vigilant every hour as if our guardian angel came down to have us report to God how we have spent our day and night every single day of our lives.

The Second Step of Humility: Not my will, But Yours O Lord

“The second step of humility is that a man loves not his own will nor takes pleasure in the satisfaction of his desires; rather he shall imitate by his actions that saying of the Lord: I have come not to do My own will, but the will of Him Who sent Me.” (John 6:38) says St. Benedict. In addition he writes of a motto, of an unknown source to me, “Consent merits punishment; constraint wins a crown” meaning that to consent to temptation is to deserve a punishment and to restrict yourself from giving in to a constraint we can win a crown. Briefly said then, St. Benedict’s second step of humility is to everywhere hold restraint from our own temptations and desires but rather to seek the will of God. Thus taking into mind the commandments of God in step one, we progress further by seeking to fulfill that commandment and not our own ways in the second step of humility.

The Third Step of Humility: He was obedient even unto death (Philippians 2:8)

The third step of humility regards obedience to our superiors. In the case of us lay people this means to be obedient to our priest, our bishop, our parents, lawful authorities, etc. all for the love of God. In this step we must submit ourselves to the yoke of Christ which He Himself bore in humility and obedience, even obedience unto death, death on a cross. And so then we must submit ourselves to God’s care, especially to the care of those who are our superiors.

The Fourth Step of Humility: Embrace Suffering Patiently and Obediently

“The fourth step of humility is that in this obedience under difficult, unfavorable, or even unjust conditions, his heart quietly embrace suffering and endures it without weakening or seeking escape.” To which St. Benedict adds from Scripture, Anyone who perseveres to the end will be saved (Matt 10:22) and to which we might add “24 Then Jesus said to his disciples: If any man will come after me, let him deny himself, and take up his cross, and follow me. 25 For he that will save his life, shall lose it: and he that shall lose his life for my sake, shall find it.” (Matthew 16:24-25) that is to say that to take up your cross and follow Christ is to save your life by choosing to give it away in servility and difficulty, but to spare ourselves from humility is to miss the entire point of our creatureliness which is the glorification of God and the honor to which we enjoy by being part of His Creation and of His holy image. Those who do not understand their place and the great benefit to have and keep a righteous and just place in God’s Creation is to throw their lives away and to lose it. Those who lose and give their life for His sake shall find it, eternally present in Him. This is the great blessing of the monastic life or those who get up and follow Him, for they have Him present in their hearts and maintain Him there by His great love in life everlasting. The saints then say, St. Benedict writes, “But in all this we overcome because of Him who so greatly loved us” (Romans 8:37) and “O God, you have tested us , you have tried us as silver is tried by fire; you have led us into a snare, you have placed afflictions on our backs” (Psalm 66:10-11) and this is greatly praised just as those who when stricken turn the other cheek to be stricken again, or when deprived of their coat offer their cloak as well, or when required to go one mile, offer to go two miles. To undergo these humiliations or sufferings patiently is to understand the depth of love of Christ’s love for us and to willingly embrace and reciprocate this love for His sake.

The Fifth Step of Humility: Confess thy Sins and Faults

The fifth step of humility is to regularly confess one’s sins, and in St. Benedict’s rule it is clear that he writes that monks confess directly to their abbot any sinful thoughts that they have in their hearts or any secret wrongdoings that they have committed against him or others. For us, this step of humility is to regularly enter into the Sacrament of Penance to confess our sins to the Lord and to the Church so that the Body of Christ, the Church, might through its ministry and binding and loosing, bring us ever close into communion with the Body of Christ so that we might one day have life everlasting with Him, the Head, Jesus. Of the same account, those seeking to fulfill this step of humility ought regularly to confess to others where they have thought poorly and unjustly of others, and in no way offer back- biting, snarky comments, or flared tempers against others. Simply thus one must avoid judging others for their sins and recognize their own sinfulness all the more strongly when witnessing a brother or sister in Christ fall into temptation. Their humility will reach out to these fallen sinners, relating to them their own faults and encouraging them by their own example to take up the Cross once again and walk the path of humility and love.

The Sixth Step of Humility: Content Yourself with Lowliness

The litany of humility reads, That I should not desire to be approved, Jesus grant me the grace to desire it, and so the sixth step of humility is to content ourselves with lowliness and to accept the lowest ranks and treatment that others have to offer. We recognize our sinfulness and our frailty and in such a manner recognize that of our own selves, left to our own devices, we are of little value, and yet not of no value because God saw in us a precious value so as to atone for our sins and bring us into His life. We are of little value because of our sins but of great value on account of the image we behold of Him. Thus we must sing with the Psalmist, “I am insignificant and ignorant, no better than a beast before You, yet I am with You always.” (Psalm 73:22-23)

The Seventh Step of Humility: Interior Mediocrity

The seventh step of humility is that we recognize and admit not only with our voice but with the fullness of our heart that we are inferior to all because of how we have been given specific, unique, and beloved gifts of God which we have squandered. They were specific to us and beautifully made for us specifically, but we spoiled God’s gifts and abused them. For this, we ought to consider ourselves inferior to others on account of how we abused ourselves through our sins and how we abused God’s gifts. To this we sin as in Psalm 22, “I am truly a worm, not a man, scorned by men and despised by the people.” And just as well “I was exalted, then I was humbled and overwhelmed with confusion.” (Psalm 88:16) or also “It is a blessing that you have humbled me so that I can learn Your commandments” (Psalm 119:71, 73). This then is to understand the fullness of why God humbles us, to learn His commandments and to join ourselves to His own nature of Self- Giving, Self-Abandoning, Self-Emptying Love. Let humility pierce our very hearts as we seek after His own Meek and Humble Heart.

The Eighth Step of Humility: To Keep the Rule

St. Benedict writes that the eighth step of humility is for a Benedictine monk to uphold the common rule of the monastery and to follow the example of his superiors. So too is it with us that we seek to keep peace in the Church, following the common example and good-will of our parish priests and bishops and this ought to be our interpretation of how to keep the rule of our parish community and of the Church as a whole.

The Ninth Step of Humility: Silence and Solitude.

A monk, ought only speak when questioned by his superiors or by others, and in all other matters hold his tongue. Do we avoid speaking ill of others, or embrace silence and solitude whenever God provides for us? Do we avoid listening to too much music or videos so as to keep our internal tongue (our mind’s tongue) silent and awaiting the contemplation of God in every moment? Remain silent in the heart and in the tongue, for God’s first language, St. John of the Cross says, is silence. So too then embrace a calm and peaceful desire for solitude, only seeking to speak when spoken too, or of pressing manners, not wasting our tongue on things that do not need to be said or saying things that ought not be said. All of St. James’ 3rd chapter in his epistle ought to be read on this matter:

1 Be not many masters, my brethren, knowing that you receive the greater judgment. 2 For in many things we all offend. If any man offend not in word, the same is a perfect man. He is able also with a bridle to lead about the whole body. 3 For if we put bits into the mouths of horses, that they may obey us: and we turn about their whole body. 4 Behold also ships, whereas they are great and are driven by strong winds, yet are they turned about with a small helm, wherever the force of the governor wills. 5 Even so the tongue is indeed a little member and boasts great things. Behold how small a fire kindles a great wood. 6 And the tongue is a fire, a world of iniquity. The tongue is placed among our members, which defiles the whole body and inflames the wheel of our nativity, being set on fire by hell. 7 For every nature of beasts and of birds and of serpents and of the rest is tamed and has been tamed, by the nature of man. 8 But the tongue no man can tame, an unquiet evil, full of deadly poison. 9 By it we bless God and the Father: and by it we curse men who are made after the likeness of God. 10 Out of the same mouth proceeds blessing and cursing. My brethren, these things ought not so to be. 11 Does a fountain send forth, out of the same hole, sweet and bitter water? 12 Can the fig tree, my brethren, bear grapes? Or the vine, figs? So neither can the salt water yield sweet.

13 Who is a wise man and endued with knowledge, among you? Let him show, by a good contestation, his work in the meekness of wisdom. 14 But if you have bitter zeal, and there be contention in your hearts: glory not and be not liars against the truth. 15 For this is not wisdom, descending from above: but earthly, sensual, devilish. 16 For where envying and contention is: there is inconstancy and every evil work. 17 But the wisdom that is from above, first indeed is chaste, then peaceable, modest, easy to be persuaded, consenting to the good, full of mercy and good fruits, without judging, without dissimulation. 18 And the fruit of justice is sown in peace, to them that make peace.

The Tenth Step of Humility: Keep Your Peace in Times of Laughter

The tenth step of humility is to avoid excessive laughter. This may sound excessive, but there is a certain extent to which jocularity, that is joking around too much, or acting a fool can be a major distraction and even arise to use making fun of holy things. Laughing at people or things which are not humorous or good-natured is to show a sort of superiority over a thing, to point to the silliness of a thing and to place one above it. So then for the lay person we must be careful not to laugh at things such as people falling down, or to put people down in our astonishment of their failures. One is entitled to joy and laughter, but not a condescending laughter which ruins humility and meekness. This is why St. Benedict enjoins, “Only a fool raises his voice in laughter” (Sirach 21:23) noting that those who are given to laughter easily often are the ones who take too lightly to the world, when their mission is divine and holy perfection.

The Eleventh Step of Humility: Speak Calmly and Modestly

As the tongue is difficult to control and lends us over to quick decisions, so we must train the heart and the tongue to speak modestly, without laughter, gently, lovingly, endearingly, and forever to be conscious of our divine destination. A wise man is known by his few words says St. Benedict. There was a Desert Father, if I recall correctly, to whom a certain bishop was coming and one monk asked him if he was not going to say something to the bishop for spiritual advice, but the Desert Father replied that if he could not teach the bishop by his own silence and contemplation that there would be nothing for him to teach the bishop with words and by speaking. This then is the model life of becoming a living word, like the Word, shining forth through example and speaking very little so as to embrace God and to show others the extent and depth to which God can occupy our minds and hearts. Desire more solitude and quietness so that you might embrace God more readily and more fully.

The Twelfth Step of Humility: Everlasting Humility and Meekness

The final step of humility is to bear all these things in one’s heart at all manners of the night and day. And in this manner the work of God will be manifest to others, and though the monk prays secretly in his closet and not publicly or does pricks his face so as to not appear to be fasting to others, his deeds and holiness will shine forth as a bright fabric and bright white shirt might readily appear to us. His holiness will shine forth, and his contrition for his sins will forever be on his mind, though he will be mindful of the great gifts God has given him, taking care not to squander them. No matter what ordinary or small deed the humble man does it will all be done with the greatest care and offering up to the Lord. In this manner then, perfect love is bloomed, says St. Benedict, a love that casts out all fear, that is to say that what was once toil and suffering has been transformed in Christ to become great joy and comfort to do the will of God. This then is the life of the soul who’s heart is united to God. - The Rule of St. Benedict and the Twelve Steps of Humility