The affix ṅīp is used in the feminine after a prātipadika (Nominal Stem) ending with the word pād when the word denotes a verse of the ṛgveda,
This debars ङीप् ॥ Thus द्विपदा ऋक् 'a Rik verse consisting of two quarter verses'; similarly त्रिपदा ऋक्, चतुष्पदा ऋक् ॥ Why do we say \when denoting a ' Rik' verse\ ? Observe द्विपदी देवदत्ता 'Devadatta (a woman) having two feet'.,