अन्त्यात् पूर्वं बह्वचः

Operational rule vidhi

In a word consisting of more than two syllables followed by ज , the acute accent (उदात्त) falls on the syllable before the last.

Word by word (padaccheda)

Left context अन्त्यात् pañcamī · ekavacanaSubstitute / term पूर्वम् prathamā · ekavacanaTarget बह्वचः ṣaṣṭhī · ekavacana

Left context Pañcamī (5th case): "after X", the operation applies to what follows (1.1.67 तस्मादित्युत्तरस्य). Also used for limits and sources.
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

अन्त्यात् पूर्वम् बह्वचः

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)

बह्वचः → पूर्वम् / अन्त्यात्

Replace bahvacaḥ with pūrvam when it comes after antyāt. Inherited words (anuvṛtti) may add further conditions.

Commentary

In a word consisting of more than two syllables followed by ज , the acute accent (उदात्त) falls on the syllable before the last.
Thus उपस꣡रजः, मन्दु꣡रजः, आमल꣡कीजः, and वड꣡वाजः (though the last two words have upapadas ending in long vowel, the accent is governed by this sutra and not the last). Why do we say "a Polysyllabic first member"? Observe दग्धजानि तृणानि ॥

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