Aitareya Āraṇyaka 1.3.3

1.3.3

tad iti pratipadyate.
tat tad iti vā annam.
annam eva tad abhiprati/padyate \
etāṃ vāva prajāpatiḥ prathamāṃ vācaṃ vyāharad ekākṣaradvya/kṣarāṃ tateti tāteti \
tathaivaitat kumāraḥ prathamavādī vācaṃ vyāhara/ty ekākṣaradvyakṣarāṃ tateti tāteti \
tayaiva tat tatavatyā vācā prati/padyate \
tad uktam ṛṣiṇā.
bṛhaspate prathamaṃ vāco agram (RV X 71,1a) ity.
etad dhy eva prathamaṃ vāco agram \
yat prairata nāmadheyaṃ dadhānā (RV X 71,1b) iti.
vācā hi nāmadheyāni dhīyante \
yad eṣāṃ śreṣṭhaṃ yad aripram āsīd (RV X 71,1c) ity.
etad dhy eva śreṣṭham e/tad aripram \
preṇā tad eṣāṃ nihitaṃ guhāvir (RV X 71,1d) iti-.
-idam u ha guhādhyātma/m.
imā devatā.
ada u āvir adhidaivatam.
ity etat tad uktaṃ bhavati \\ 3 \\

He begins with tad, this, (the first word of the first hymn, tad id âsa). Verily 'this, this' is food, and thus he obtains food.

Pragâpati indeed uttered this as the first word, consisting of one or two syllables, viz. tata and tâta (or tat). And thus does a child, as soon as he begins to speak, utter the word, consisting of one or two syllables, viz. tata and tâta (or tat). With this very word, consisting of tat or tatta, he begins.

This has been said by a Rishi (Rv. X, 71, 1):--

'O Brihaspati, the first point of speech;'--for this is the first and highest point of speech.

'That which you have uttered, making it a name;'--for names are made by speech.

'That (name) which was the best and without a flaw;'--for this is the best and without a flaw.

'That which was hidden by their love, is made manifest;'--for this was hidden in the body, viz. those deities (which enter the body, Agni as voice, entering the mouth, &c.); and that was manifest among the gods in heaven. This is what was intended by the verse.