The feminine affixes are not used after the stems called ṣad -- ṣṇāntā ṣaṭ [[1.1.24]] and after svasra etc.,
This prohibits all feminine affixes that would otherwise have presented themselves. Thus पञ्च ब्राह्मण्यः 'the five Brahmani ladies'. So also सप्त, नव, दश &c are feminine as well as masculine. The following words belong to the Svasradi class:- स्वसा 'a sister', दुहिता 'a daughter'; ननान्दा 'a husband's sister', याता 'a husband's brother's wife', माता 'a mother', तिस्रः 'three'. चतस्रः 'four'.,