What is the meaning of Pali word "Apannaka"

dayāpanna:

There is no real contradiction in the various translation quoted and they all fit for the meaning in context as well.

Panna/paṇṇa: bend down, ~ka downbendig, upwardly, falling.

The "bet" idea of Nyom Chris, as a relative, fit's also in relation of "giving into something". As all path factors, especially the initial, right view, are leading to heardwood, security, also to saw that the path is a secure, fits here well, and since it requires faith at first place, "good bet, secure bet" is totaly fine and a good rendering as well.

apaṇṇa: certain, true, secure. ~ka: ~ing

May non be an ''Apaññaka'' toward the Sublime juwels and takes on right thoughts, not wrong, like mostly if worldling, panna:

"And how is one made impure in three ways by mental action? There is the case where a certain person is covetous. He covets the belongings of others, thinking, 'O, that what belongs to others would be mine!' He bears ill will, corrupt in the resolves of his heart: 'May these beings be killed or cut apart or crushed or destroyed, or may they not exist at all!' He has wrong view, is warped in the way he sees things: 'There is nothing given, nothing offered, nothing sacrificed. There is no fruit or result of good or bad actions. There is no this world, no next world, no mother, no father, no spontaneously reborn beings; no brahmans or contemplatives who, faring rightly & practicing rightly, proclaim this world & the next after having directly known & realized it for themselves.' This is how one is made impure in three ways by mental action...Furthermore, as a result of being endowed with these ten courses of unskillful action, [rebirth in] hell is declared, [rebirth in] an animal womb is declared, [rebirth in] the realm of hungry shades is declared — that or any other bad destination. ''AN 10.176''

''Sīlena sugatiṃ yanti.''
Through virtue they go to a good bourn.
''Sīlena bhoga-sampadā.''
Through virtue is wealth attained.
''Sīlena nibbutiṃ yanti.''
Through virtue they go to Liberation.
''Tasmā sīlaṃ visodhaye.''
Therefore we should purify our virtue.

[Note that this is not given for any ''Āpaṇa'', market, bazaar... but for Apannaka, for release, if possible to take]

I think the a prefix implies the negative -- so a more literal translation might be "not a bet" (i.e. it's a certainty ... it is not chancy).

It obviously cannot be "guaranteed" because the moral realm is never guaranteed; per MN 136, MN 117, etc. Regardless of what "apaṇṇaka" means; I think a "safe bet" is the most accurate meaning, based on Dhamma principles. The idea of "incontrovertible" appears to slander the Dhamma.

For example, moral people who hold the follow view can still suffering when their mother & father die because they still believe in mother & father:

‘There is what is given and what is offered and what is sacrificed; there is fruit and result of good and bad actions; there is this world and the other world; there is mother and father; there are beings who are reborn spontaneously; there are good and virtuous recluses and brahmins in the world who have themselves realised by direct knowledge and declare this world and the other world.’

MN 117, a later addition, written by an arahant, properly says the above is non-noble defiled right view siding with merit & not siding with liberation. MN 117 was required to be written to straighten out other later additions, such as MN 60, which falsely say worldly right view has guaranteed results.

The book "The Notion of Ditthi in Theravada Buddhism: The Point of View" by Paul Fuller states that the meaning of the word "Apaṇṇaka" as "incontrovertible".

"A sutta called Diṭṭhi-apaṇṇaka paṭipadā-sutta at A II 76 states that when a bhikku is possessed of four things he has entered on the path to the 'incontrovertible' (apaṇṇaka) and the destruction of the āsavās."

~ Cited from: The Notion of Ditthi in Theravada Buddhism: The Point of View

In the Sinhalese translation of Jātaka Pāli-Khuddaka Nikāya, the phrase "Apaṇṇaka paṭipadā" is translated as "නිසි මඟ [Nisi ma(n)ga]" which means "appropriate path/way". In the same translation and in the translation of Apaṇṇaka Vagga of Aṅguttara Nikāya, the word "consistent" ["අවිරුද්ධ" in Sinhalese] used for the word "Apaṇṇaka".

"බෝධිසත්වාදී නුවණැති සමහර කෙනෙක් අවිරුද්ධ වූ කාරණය (අපණ්ණක ප්‍රතිපදාව = නිසි මඟ) ගත්හ."

~ Cited from: Apaṇṇaka Vagga, Jātaka Pāli, Khuddaka Nikāya