द्विगुरेकवचनम्

All affixes after the verb गाङ् 'to study' and the verb कुट् 'to be crooked' and the rest, are as if they had an indicatory ङ् (ङित्), except those affixes which have an indicatory ञ् (ञित्) or ण् (णित्).
The word एकवचन is a genitive Tat-purusha compound meaning 'the expression for one,' that is to say, it expresses the sense of unity. The rule therefore, enjoins that the sense inherent in a Dvigu compound is that of unity.

This is confined to Samahara Dvigu i.e., an aggregate compound taken in a collective sense. As, पञ्चगवं 'an aggregate of five cows', पञ्चपली (IV.1.21.). The sense of Dvigu being that of one, it follows that it retains the singular number even when further modified by other affixes, and used as an attributive and though no longer a Dvigu, as, पञ्चपूलीयं शोभना ॥