षः प्रत्ययसय

The initial ष् of an affix gets the name of इत् and is rejected. Thus by Rule 3.1.145 (शिल्पिनि ष्वुन्) the affix ष्वुन् is added to a verb to indicate proficient in the art expressed by the verb. The ष् and न् are इत् and अक् takes the place of वु (VII. I.1), युवोरनाकौ). Thus नृत् + ष्वुन् = नर्त् + अक् = नर्तकः 'a dancer' (by profession); fem. नर्तकी 4.1.41, षिद्गौरादिभ्यश्च 'words formed by affixes having an indicatory ष् take the affix ङीष् in the feminine'): so also रजकः, fem. रजकी.

The initial ष् of an affix only is इत् and not every initial ष्. Thus not in षोडः 'six,' or षडिकः ॥ The ष् must be initial, therefore it is not इत् in the affix टिषच् in अविमह्योष्टिषच्, (Un I. 45) as अविषः 'an ocean', महिषः 'a buffalo.',