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1580s, from French moustache (15c.), from Italian mostaccio, from Medieval Greek moustakion, diminutive of Doric mystax (genitive mystakos) "upper lip, mustache," related to mastax "jaws, mouth," literally "that with which one chews," from PIE root *mendh- "to chew" (see mandible).
Borrowed earlier (1550s) as mostacchi, from the Italian word or its Spanish derivative mostacho. The plural form of this, mustachios, lingers in English. 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."
hair grown on the upper lip by men. The wearing of mustaches, like beards, has been since antiquity a reflection of such factors as climate (local or temporal), custom, religious belief, and personal taste. It was usual in the past to make no distinction between a mustache and other facial hair such as a beard or whiskers, as these were usually worn together. As early as 2650 BC, however, Egyptian artifacts show a pencil-line mustache with no beard