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.
rapture n.
c. 1600, "act of carrying off" as prey or plunder, from rapt + -ure, or else from French rapture, from Medieval Latin raptura "seizure, rape, kidnapping," from Latin raptus "a carrying off, abduction, snatching away; rape" (see rapt). The earliest attested use in English is with women as objects and in 17c. it sometimes meant rape (v.), which word is a cognate of this one.
The sense of "spiritual ecstasy, state of mental transport or exaltation" is recorded by c. 1600 (raptures). The connecting notion is a sudden or violent taking and carrying away. The meaning "expression of exalted or passionate feeling" in words or music is from 1610s.