Green’s Dictionary of Slang

(orig. US) cunnilingus.

c.1931		in P. Smith Letter from My Father (1978) 256: Few American men understood the fine art of preliminary stimulation, how necessary it was for the female and how ‘cunt-lapping’ helped.
1971		J. Jones Merry Month of May (2004) 55: His own young porno collection had swung more and more toward [...] material having to do with cunt-lapping.
1998		‘Bill E. Goodhead’ Nubile Treat 🌐 From a playful little game, the cunt-lapping had become very much in earnest.