स्यश्छन्दसि बहुलम्

Operational rule vidhi

In the derivation of the Vedic words, the सुँ-प्रत्यय attached to the प्रथमा-एकवचन of the word त्यद् might or might not be removed when followed by a हल् in the context of संहिता.

Word by word (padaccheda)

Substitute / term स्यः prathamā · ekavacanaRight context छन्दसि saptamī · ekavacanaSubstitute / term बहुलम् prathamā · ekavacana

Substitute / term Prathamā (1st case): in operational rules, the substitute or the thing introduced; in definitions, the term or its referent.
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").

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

स्यः छन्दसि बहुलम्

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

Commentary

In the छन्दस् , the case-affix of the nominative singular is diversely elided after स्य , when a consonant follows it.
Thus उत स्य वाजी क्षिपणिं तुरण्यति ग्रीवायां बद्धो अपिकक्ष आसनि (Rig IV. 40.4), एष स्य ते मधुर्मी इन्द्र सोमः (Rig IX. 87.4) ॥ Sometimes it does not take place: as यत्र स्यो निपतेत् ॥ The स्य means 'he'.

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