विभाषा वेण्विन्धानयोः

Operational rule vidhi

The acute accent is optionally on the first syllable of वेणु and इन्धान.

Word by word (padaccheda)

Substitute / term prathamā · ekavacanaTarget वेणु- इन्धानयोः ṣaṣṭhī · dvivacana

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

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

Full reading

वेणु-इन्धानयोः

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)

वेणु- इन्धानयोः → optional

Replace veṇu-indhānayoḥ with vibhāṣā, optionally. Inherited words (anuvṛtti) may add further conditions.

Commentary

The acute accent is optionally on the first syllable of वेणु and इन्धान।
Thus वे꣡णुः or वेणुः꣡; इ꣡न्धानः or इन्धा꣡नः or इन्धानः꣡ ॥ The word वेणु is derived by the Unadi affix णु (III.38), which being a नित् would always have acute on the first. This allows an option. The word इन्धान, if it is formed by चानश् it will have the accent on the final. If it is considered to be formed by शानच्, the affix being a sarvadhatuka is anudatta, and as it replaces udatta final of the root, it becomes udatta 6.1.161, and thus इन्धान gets acute on the middle. It would never have acute on the first syllable, the present rule ordains that also. When वेणु is used as an -upamana वेणुरिव वेणुः, then it is invariably acutely accented on the first 6.1.204.

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