In forming the feminine with the affix ṅīp , n is optionally the substitute of the final i of pati when the latter is preceded by another vowel.,
The word सपूर्वस्य means when the word पति is not an upasarjana, but stands at the end of a compound. Thus वृद्धपतिः or वृद्धपत्नी; स्थूलपतिः or स्थूलपत्नी ॥ This is an example of aprapta-vibhasha. Because it is free from the limitations of 'yajna-sanyoga' of the last sutra. Why do we say when it is preceded by another word? Observe पतिरियं ब्राह्मणी ग्रामस्य, this Brahman lady is the mistress of the village.' Here the feminine is पति and not पत्नी ॥,