बहुवचने झल्येत्

Operational rule vidhi

The last letter of an अदन्त अङ्ग gets an एकारादेश when followed by a सुप्-प्रत्यय which begins with a झल letter and which represents बहुवचन.

Word by word (padaccheda)

Right context saptamī · ekavacanaRight context saptamī · ekavacanaSubstitute / term एत् prathamā · ekavacana

Right context Saptamī (7th case): "when X follows", the operation applies to what precedes (1.1.66 तस्मिन्निति निर्दिष्टे पूर्वस्य). Also a condition or domain ("in the sense of").
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, dashed ones pratyāhāras (names for classes of sounds or affixes). Hover or tap one to see its card.

Full reading

एत्

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

Commentary

Before a case-ending beginning with भ् or स् (literally a consonant of the झल् प्रत्यहार) in the plural, ए is substituted for the final अ of Nominal-stem.
As वृक्षेभ्यः, प्लक्षेभ्यः, वृक्षेषु, प्लक्षेषु ॥ Why in the Plural? Observe वृक्षाभ्याम् प्लक्षाभ्याम् ॥ Why before a case-affix beginning with a झल् consonant? Observe वृक्षाणाम् (the lengthening here is by 6.4.3). Why a case-affix? Observe यजध्वम्, पचध्वम् ॥

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