From Wiktionary, the free dictionary
From the dative of Proto-Indo-European *-tus, whence also -तुम् (-tum), from the accusative.
-तवे • (-tave) (Vedic)
- Forms infinitives from roots.
- कृ (kṛ, root) + -तवे (-tave) → कर्तवे (kártave, “to do”, infinitive of कृ (kṛ))