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.
also feoff, 1610s, from French fief (12c.) "a 'feud,' possession, holding, domain; feudal duties, payment," from Medieval Latin feodum "land or other property whose use is granted in return for service," widely said to be from Frankish *fehu-od "payment-estate," or a similar Germanic compound, in which the first element is from Proto-Germanic *fekhu, making it cognate with Old English feoh "money, movable property, cattle" (see fee). Second element perhaps is similar to Old English ead "wealth" (see Edith).
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Definitions of enfeoff from WordNet
put in possession of land in exchange for a pledge of service, in feudal society;
He enfeoffed his son-in-law with a large estate in Scotland