There is the elision of the affix vi when reduced to the single letter v,
The affix वि includes क्विप्, क्विन्, ण्वि &c. In all these, the real affix is व्, which being an aprikta 1.2.41, is elided. Thus ब्रह्महा, भ्रूणहा 3.2.87. Here the affix क्विप् is elided. So also घृतस्पृक्, तैलस्पृक् 3.2.58. Here the affix क्विन् is elided. So also अर्धभाक्, पादभाक्, तुरीयभाक् 3.2.62. Here the affix ण्वि is elided.
Why do we say \of an aprikta-an affix consisting of a single letter\? Observe दर्विः formed by the affix विन् (वि being the real affix); so also जागृविः formed क्विन्, see Unadi Sutras IV. 53. 44. No root can become a noun unless some krit affix is added to it (see 1.2.45 and 1.2.46); hence the necessity of these imaginary affixes, in order to raise certain roots bodily, without any change, to the rank of nouns--from Dhatu to a Pratipadika the way lies only through an affix. And though these imaginary affixes are after all totally elided, yet by 1.1.62, they leave their characteristic mark behind, namely the derivative word becomes a nominal stem &c. Thus च्वि words are adverbs (Gati) and Indeclinables.,