Of water, "splash gently, flow against" first recorded 1823, based on similarity of sound. Figurative use of lap (something) up "receive it eagerly" is by 1890. Related: Lapped; lapping. The noun meaning "liquid food; weak beverage" is from 1560s.
"compound of fruits and spices used as a condiment in the East Indies," 1813, said to be from Hindi chatni "to lick."
"lustful man, man given to excessive sexual indulgence," late 12c., from Old French lecheor (Modern French lécheur) "one living a life of debauchery," especially "one given to sexual indulgence," literally "licker," agent noun from lechier "to lick;" also "to live in debauchery or gluttony," from Frankish *likkon or some other Germanic source, from Proto-Germanic *likkojan "to lick" (from PIE root *leigh- "to lick"). The Old French feminine form was lechiere. Middle English, meanwhile, had lickestre "female who licks;" figuratively "a pleasure seeker," literally "lickster," with -ster. In 18c. sometimes leacher (Bailey), along with leacherous, leachery.
1884 (by 1845 in German, 1824 in medical Latin), from Latin cunnus "vulva, female pudenda" (also, vulgarly, "a woman") + lingere "to lick" (from PIE root *leigh- "to lick"). Latin cunnus is of disputed origin, perhaps literally "gash, slit," from PIE *sker- (1) "to cut," or [Watkins] literally "sheath," from PIE *kut-no-, from root *(s)keu- "to cover, conceal."
The Latin properly would mean "one who licks a vulva," but it is used in English in reference to the action. The verb ought to be *cunnilingue. As an agent-noun, Fletcher has lick-twat (1656). Gordon Williams ["A Dictionary of Sexual Language and Imagery in Shakespearean and Stuart Literature," 1994] writes that Nicolas Chorier's 17c. "Satyra Sotadica" "relates how Gonsalvo of Cordova, as an old man, would lick his mistress's middle parts, which he called, with a geographical pun, going to Liguria" (from Latin ligurio "to lick").
Cunnilingus was a very familiar manifestation in classical times; ... it tends to be especially prevalent at all periods of high civilization. [Havelock Ellis, "Studies in the Psychology of Sex," 1905]
Dutch slang has a useful noun, de befborstel, to refer to the mustache specifically as a tool for stimulating the clitoris; probably from beffen "to stimulate the clitoris with the tongue."