वच उम्

Operational rule vidhi

The augment उ is added after the अ of वच् in the Aorist अङ्.

Word by word (padaccheda)

Target वचः ṣaṣṭhī · ekavacanaSubstitute / term उम् prathamā · ekavacana

Target Ṣaṣṭhī (6th case): names what gets replaced, "in place of X" (1.1.49 षष्ठी स्थानेयोगा).
Substitute / term Prathamā (1st case): in operational rules, the substitute or the thing introduced; in definitions, the term or its referent.

Dotted words are technical terms. Hover or tap one to see its card.

वचः उम्

Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.

As a rewrite rule (sketch from case endings)

वचः → उम्

Replace vacaḥ with um. Inherited words (anuvṛtti) may add further conditions.

The augment उ is added after the अ of वच् in the Aorist अङ्।
As अवोचत्, अवोचताम्, अवोचन् ॥ See 3.1.52.

Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.