8.3.106
पूर्वपदात्
Operational rule vidhi
In the छन्दस् (Vedas), ष् is substituted for the स् when it stands in the beginning of a second word, preceded by a word ending in इ etc.
Word by word (padaccheda)
Left context पूर्वपदात् 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.
Full reading
पूर्वपदात्
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 (Vedas), ष् is substituted for the स् when it stands in the beginning of a second word, preceded by a word ending in इ etc.
The words छन्दसि and एकेषां are both understood here. Thus द्विषन्धिः or द्विसन्धिः, त्रिषन्धिः or त्रिसन्धिः; मधुष्ठानम् or मधुस्थानम्, द्विसाहस्रं चिन्वीत or द्विषाहस्रं चिन्वीत ॥
The word पूर्वपद here means the first member of a compound word as well as the prior word other than that in a compound. Thus त्रिःषमृद्धत्वाय or त्रिःसमृद्धत्वाय ॥
Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.