2.4.21 उपज्ञोपक्रमं तदाद्याचिख्यासायाम्

Word by word (padaccheda)

Substitute / term उपज्ञा- उपक्रमम् prathamā · ekavacanaRight context तद्- आदि- आचिख्यासायाम् saptamī · 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").

Full reading

उपज्ञा-उपक्रमम् तद्-आदि-आचिख्यासायाम्

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

Commentary

A तत्-पुरुष compound ending with the words उपज्ञा 'invention' and उपक्रम 'commencement' is neuter in gender, when it is intended to express the starting point of a work which is first invented or commenced.
As, पाणिन्युपज्ञमाकालापकं व्याकरणम् 'the grammars Kalapa &c., had their commencement with Panini's invention'; व्याड्युपज्ञं दुष्करणं 'Vyadi, invented Dushkarana'; आढ्योपक्रम प्रासादः 'the palace is an invention of rich folks'; मन्दोपक्रमाणि मानानि 'the measures are the invention of king Nanda.'

Of course, when it has not this sense, the neuter gender is not employed; as देवदत्तोपज्ञो रथः 'the chariot made by Devadatta,' यज्ञदत्तोपक्रमो रथः 'the chariot commenced by Yajnadatta.' So also the sense may be that of invention &c., but when these words are not employed, the neuter gender is not used; as वाल्मीकिश्लोकाः 'the slokas invented by Valmiki.' N. P. Prof. Bohthlingk gives पाणिन्युपज्ञमकालकं व्याकरणम् 'The Grammar omitting the time of day is the work invented by Panini, 6.2.14.

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