Longman Dictionary of Contemporary English
The Collaborative International Dictionary
[F. en-, L. in.] A prefix signifying in or into, used in many English words, chiefly those borrowed from the French. Some English words are written indifferently with en-or in-. For ease of pronunciation it is commonly changed to em-before p, b, and m, as in employ, embody, emmew. It is sometimes used to give a causal force, as in enable, enfeeble, to cause to be, or to make, able, or feeble; and sometimes merely gives an intensive force, as in enchasten. See In-.
A prefix from Gr. ? in, meaning in; as, encephalon, entomology. See In-.
Douglas Harper's Etymology Dictionary
word-forming element meaning "in; into," from French and Old French en-, from Latin in- "in, into" (see in- (2)). Typically assimilated before -p-, -b-, -m-, -l-, and -r-. Latin in- became en- in French, Spanish, Portuguese, but remained in- in Italian.\n
\nAlso 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.
pre. 1 in, into, on, onto 2 covered 3 caused 4 as an intensifier
Usage examples of "en-".
A British dry-cargo vessel had been preparing to en-ter the Maas Estuary for Rotterdam when the 0900 call was made from the Freya to Maas Control.