Word and Meaning — Vyākaraṇa & Nirukta
Once the sound is exact, the next question is what the words are doing. Two limbs answer it: grammar analyses a word forward, etymology analyses it backward to its root.
Pāṇini's machine
About four thousand sūtras, ordered so that each one applies only after the conditions of the last are set. Roots (dhātu), suffixes (pratyaya), and case-relations (kāraka) generate the entire language. Nothing in it depends on a prior sentence being true.
Nirukta — the word unpacked
Yāska’s Nirukta, built on the Nighaṇṭu word-lists, asks of a Vedic word not only what it means but why it means it — tracing it to a root and a reason. It is how agni is read as agre nayati (he who leads to the front), and how an obscure hymn-word becomes a deity’s function.
Grammar without etymology gives correct but weightless words. Etymology without grammar gives speculation. The tradition insists on both.