The affix ghañ comes after the roots 1. tṝ 'to cross' 2. stṝ 'to spread, to cover', when the upasarga ava is in composition with them and when the word so formed is an appellative related to the verb either as an instrument or as a location.,
This supersedes घ । The ञ् is indicatory and causes the vriddhi of ॠ 7.2.115 and is also for the sake of regulating the accent 6.1.195, 6.1.197. The indicatory घ् is useful in the subsequent aphorism where it changes the palatals into gutturals. Thus अवतारः 'the descent (or incarnation of a diety); अवस्तारः 'a screen round a tent'.
How do we apply अवतार also in phrases like अवतारो नद्याः 'the descent of rivers', for here the word avatara is not an appellative? This use is also allowed, because the anuvritti of the word प्राय is understood here also; so that those words avatara &c. may be employed in senses other than appellative.,