envenom (v.)

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.

mid-13c., venim, venym, "poison secreted by some animals and transferred by biting," from Anglo-French and Old French venim, venin "poison; malice," from Vulgar Latin *venimen (source also of Italian veleno, Spanish veneno), from Latin venenum "poison," earlier (pre-classical) "drug, medical potion," also "charm, seduction," probably originally "love potion," from PIE *wenes-no-, from root *wen- (1) "to desire, strive for." Variously deformed in post-Latin languages, apparently by dissimilation. Modern spelling in English from late 14c. The meaning "bitter, virulent feeling or language" is first recorded c. 1300.