According to the online Etymology Dictionary the word cunnilingus dates back to 1887 and was derived ‘from Latin cunnus “vulva” (see cunt) + lingere “to lick” (see lick (v.)). The Latin properly would mean “one who licks a vulva,” but it is used in English in reference to the action, not the actor. The verb ought to be *cunnilingue.’

– www.etymonline.com