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."

Proto-Indo-European root meaning "to lick." It forms all or part of: cunnilingus; lecher; lichen; lick.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit ledhi "he licks," Armenian lizum "I lick," Greek leikhein "to lick," Latin lingere "to lick," Old Irish ligim "I lick," Welsh llwy "spoon," Old English liccian "to lick."

Proto-Indo-European root meaning "to cover, conceal."

It forms all or part of: chiaroscuro; cunnilingus; custody; cutaneous; cuticle; -cyte; cyto-; hide (v.1) "to conceal;" hide (n.1) "skin of a large animal;" hoard; hose; huddle; hut; kishke; lederhosen; meerschaum; obscure; scum; skewbald; skim; sky.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit kostha "enclosing wall," skunati "covers;" Greek kytos "a hollow, vessel," keutho "to cover, to hide," skynia "eyebrows;" Latin cutis "skin," ob-scurus "dark;" Lithuanian kiautas "husk," kūtis "stall;" Armenian ciw "roof;" Russian kishka "gut," literally "sheath;" Old English hyd "a hide, a skin," hydan "to hide, conceal; Old Norse sky "cloud;" Old English sceo "cloud;" Middle High German hode "scrotum;" Old High German scura, German Scheuer "barn;" Welsh cuddio "to hide."

1590s, "covering into which both hands may be thrust to keep them warm," from Dutch mof "a muff," shortened from Middle Dutch moffel "mitten, muff," from  French moufle "mitten," from Old French mofle "thick glove, large mitten, handcuffs" (9c.), from Medieval Latin muffula "a muff," a word of unknown origin.

The muff was introduced into France toward the close of the sixteenth century, and soon after into England. It was used by both men and women, and in the seventeenth century was often an essential part of the dress of a man of fashion; but it is now exclusively an article of female apparel. [Century Dictionary]

Meaning "vulva and pubic hair" is from 1690s; muff-diver "one who performs cunnilingus" is from 1935.

Old English etan (class V strong verb; past tense æt, past participle eten) "to consume food, devour, consume," from Proto-Germanic *etan (source also of Old Frisian ita, Old Saxon etan, Middle Dutch eten, Dutch eten, Old High German ezzan, German essen, Old Norse eta, Gothic itan), from PIE root *ed- "to eat."

Transferred sense of "corrode, wear away, consume, waste" is from 1550s. Meaning "to preoccupy, engross" (as in what's eating you?) first recorded 1893. Slang sexual sense of "do cunnilingus on" is first recorded 1927. The slang phrase eat one's words "retract, take back what one has uttered" is from 1570s; to eat one's heart out is from 1590s; for eat one's hat, see hat. Eat-in (adj.) in reference to kitchens is from 1955. To eat out "dine away from home" is from 1930.