True versus Correct in uttered speech

The Pali in MN 58 is:

In the same way, prince, the Realized One does not utter speech that he knows to be untrue, false and pointless, and which is disliked by others. (Sujato translation)

Evameva kho, rājakumāra, yaṁ tathāgato vācaṁ jānāti abhūtaṁ atacchaṁṁ anatthasaṁhitaṁ sā ca paresaṁ appiyā amanāpā, na taṁ tathāgato vācaṁ bhāsati.

The word 'bhūta' is used in many ways in the suttas, such as:

Mendicants, do you see that this has come to be?”

Bhūtamidanti, bhikkhave, passathā”ti?

MN 38

Therefore, a better translation of "abhūtaṁ" in MN 58 would point to matters that "have not come to exist", "do not exist" or are "non-existent", in short, "unfactual/unevidenced/unsustantiated". Alternate translations are:

Even so, Prince, whatever speech the Tathāgata knows to be not fact, not true, not connected with the goal, and that is not liked by others, disagreeable to them, that speech the Tathāgata does not utter (I.B. Horner)

So too, Prince, such speech as a Tathāgata knows does not represent what is [does not represent what has come to be], does not accord with reality, and is unconnected with good (Nyanamoli Thera)

In the case of words that the Tathagata knows to be unfactual, untrue, unbeneficial (or: not connected with the goal), unendearing & disagreeable to others, he does not say them. (Thanissaro)

The other relevant Pali word in MN 58 is taccha. I was going to suggest 'taccha' has a moral quality, such as meaning 'honest', because it is found in Snp 2.9, as follows:

With what morality, what conduct, fostering what deeds, would a person lay the foundations right and reach the highest goal?

Delighting in the teaching, enjoying the teaching, standing on the teaching, investigating the teaching, they’d never say anything that degraded the teaching, but would be guided by genuine words well-spoken (tacchehi nīyetha subhāsitehi).

However, the dictionary says taccha is derived from tathā + ya. The word 'tathā' appears to mean 'real', such as found in the following context:

Mendicants, these four things are real, not unreal, not otherwise. Cattārimāni, bhikkhave, tathāni avitathāni anaññathāni.

What four? ‘This is suffering’ … ‘This is the origin of suffering’ … ‘This is the cessation of suffering’ … ‘This is the practice that leads to the cessation of suffering’ … These four things are real, not unreal, not otherwise.

SN 56.20

The above said, possibly taccha/tathā do have a moral quality, because what is described as 'tathā' in SN 56.20 are verbal statements by the Buddha rather than the mere natural lawful facts of suffering, origin, cessation & path.

In conclusion, without doing anymore research, I would speculate 'bhuta' means 'existent' and 'taccha' is a moral reflection upon what is 'existent' and thus means 'truthful/honest'.

In the same way, prince, the Realized One does not utter speech that he knows to be unfactual/unevident, dishonest and unbeneficial, and which is disliked by others.

(DD translation)

Based on the PTS dictionary entries for taccha and bhūta:

• Taccha: ... true, real, justified, usually in combn w. bhūta. bhūta taccha tatha

  If it's usually "in combination" then perhaps it's not a separate meaning but some kind of compound meaning -- like "immensely huge" in English, two words that are similar, adjacent in meaning, and adjacent in the combined phrase

• Bhūta seems to mean -- natural, existing (in animate or inanimate nature)

The dictionary entry for taccha says that it's "derived from tathā+ya=tath -- ya" meaning "as it is," Sanskrit "tathya".

The "tathā" root is found elsewhere, for example:

• "tathata" (suchness) -- see What is tathata?
• tathagata -- see Why does the Buddha call himself the Tathāgata?

Used together I guess the two words might translate as, "something which is so, in nature/existence".