embouchure n.

word-forming element meaning "in; into," from French and Old French en-, from Latin in- "in, into" (from PIE root *en "in"). Typically assimilated before -p-, -b-, -m-, -l-, and -r-. Latin in- became en- in French, Spanish, Portuguese, but remained in- in Italian.

Also used with native and imported elements to form verbs from nouns and adjectives, with a sense "put in or on" (encircle), also "cause to be, make into" (endear), and used as an intensive (enclose). Spelling variants in French that were brought over into Middle English account for parallels such as ensure/insure, and most en- words in English had at one time or another a variant in in-, and vice versa.

French, literally "mouth" (Old French boche, 11c.), from Latin bucca "cheek," which in Late Latin replaced os (see oral) as the word for "mouth" (and also is the source of Italian bocca, Spanish boca). De Vaan writes that "The meaning 'mouth' is secondary, and was originally used in a derogatory way." It is perhaps from Celtic, Germanic, or a non-IE substrate language.

The French word was borrowed in English in various senses, such as "king's allowance of food for his retinue" (mid-15c.); "mouth" (1580s); "metal plug for a cannon's vent" (1862; the verb in this sense is from 1781).