In the mantra literature,the affix ṇivan comes after the words 1. śvetavaha 2.ukthaśa 3. puroḍāś ,
The above words contain both the verb and the upapada; the fact of their being so given indicates that there is some irregularity in the application of the affix.
Thus the affix ण्विन् comes after the verb वह् preceded by the upapada श्वेत as denoting an agent, while the force of the whole word so formed denotes an object. As श्वेता एनं वहन्ति = श्वेतवाह् nom. sing. श्वेतवाः 'a name of Indra' (whom white horses carry).
The affix ण्विन् is applied to the verb शंस् 'to praise' when preceded by the word उक्थ as object or instrument; and then the nasal is irregularly dropped. As उक्थानि उक्थैर्वा शंसति = उक्थशास्, nom. sing. उक्थशाः (Rig. Ved. II. 39. 1.) 'a reciter of hymns, the name of the sacrificer'.
The ण्विन् is applied after the verb दाशृ 'to give', preceded by पुरो, and द is changed into ड, the force of the whole word denoting an object. As पुरो दाशन्ति एनं = पुरोडाश्, nom. sing. पुरोडाः (Rig. Ved. III. 28. 2) 'an offering'.
Vart:--The augment उस् is added to the words श्वेतवाह् &c., when the pada affixes follow. Thus before pada terminations श्वेतवाह् becomes श्वेतवस् । Therefore its Instrumental dual is श्वेतवोभ्याम्, pl. श्वेतवोभिः ।
The augment उस् is not applied before सर्वनामस्थान and भ terminations. As श्वेतवाहौ, श्वेतवाहः ।,