178. Final r

Final र् r, in general, shows the same form which स् s would show under the same conditions.

a. Thus, it becomes visarga when final, and a sibilant or visarga before an initial surd mute or sibilant (170): thus, rudatī punaḥ, dvās tat, svàç ca, catúçcatvāriṅçat; and (111c, d) prātastána, antastya, catuṣṭaya, dhūstva; prātaḥ karoti, antaḥpāta.

b. But original final r preceded by a or ā maintains itself unchanged before a sonant: thus, punar eti, prātarjit, ákar jyótiḥ, áhār dā́mnā, vārdhi.

c. The r is preserved unchanged even before a surd in a number of Vedic compounds: thus, aharpáti; svàrcanas, svàrcakṣas, svàrpati, svarṣā́, svàrṣāti; dhūrṣád, dhūrṣah; pū́rpati, vārkāryá, āçī́rpada, punartta; and in some of these the r is optionally retained in the later language. The RV. also has āvar támaḥ once in sentence-combination.

d. On the other hand, final ar of the verb-form āvar is changed to o before a sonant in several cases in RV. And r is lost, like s, in one or two cases in the same text: thus, akṣā índuḥ, áha evá.