en- (1) Look up en- at Dictionary.com
word-forming element meaning "in, into," from French and Old French en-, from Latin in- "in, into" (see in- (2)). Typically assimilated to -p-, -b-, -m-, -l-, and -r-.

Also used with native elements to form verbs from nouns and adjectives, "put in or on" (encircle), also "cause to be, make" (endear), and used as an intensive (enclose). Spelling variants in French that were brought over into Middle English account for parallels such as assure/ensure/insure.
en- (2) Look up en- at Dictionary.com
word-forming element meaning "near, at in, on, within," from Greek en "in," cognate with Latin in (see in), and with en- (1). Typically assimilated to -p-, -b-, -m-, -l-, and -r-.