224. Irregularities of combination

Irregularities of combination are:

a. The vowel ṛ is not lengthened after the loss of the h-element: thus, dṛḍhá, tṛḍhá, bṛḍhá (the only cases; and in the Veda their first syllable has metrical value as heavy or long).

b. The roots vah and sah change their vowel to o instead of lengthening it: thus, voḍhám, voḍhā́m, voḍhár, sóḍhum. But from sah in the older language forms with ā are more frequent: thus, sāḍhá, áṣāḍha (also later), sā́ḍhar. The root tṛṅh changes the vowel of its class-sign na into e instead of lengthening it: thus, tṛṇeḍhi, tṛṇéḍhu, atṛṇet (the grammarians teach also tṛṇehmi and tṛṇekṣi: but no such forms are quotable, and, if ever actually in use, they must have been made by false analogy with others).

c. These anomalous vowel-changes seem to stand in connection with the fact that the cases showing them are the only ones where other than an alterant vowel (180) comes before the lingualized sibilant representative of the h. Compare ṣóḍaça etc.

d. Apparently by dissimilation, the final of vah in anomalous compound anaḍvah is changed to d instead of ḍ: see 404.