द्वित्रिभ्यां ष मूर्ध्नः

Operational rule vidhi

The affix ष comes after a बहुव्रीहि समास ending in मूर्ध्न् and preceded by 1. द्वि and 2. त्रि.

Word by word (padaccheda)

Left context द्वित्रिभ्याम् pañcamī · dvivacanaWord ष Left context मूर्ध्नः pañcamī · ekavacana

Left context Pañcamī (5th case): "after X", the operation applies to what follows (1.1.67 तस्मादित्युत्तरस्य). Also used for limits and sources.
Word Case not marked in the source data.

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Full reading

द्वित्रिभ्याम् ष मूर्ध्नः

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

Commentary

The affix ष comes after a बहुव्रीहि समास ending in मूर्ध्न् and preceded by 1. द्वि and 2. त्रि।
Thus द्विमूर्धः, त्रिमूर्धः ॥ The feminine is formed by ङीष् and the accent is regulated by 6.2.197.

Why do we say "preceded by dvi and tri?" Observe उच्चैर्मूर्धा ॥

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