en- 1 (also em-)
1 forming verbs (added to nouns) expressing entry into the specified state or location : engulf | embed.
2 forming verbs (added to nouns and adjectives) expressing conversion into the specified state (as in encrust, ennoble).
• often forming verbs having the suffix -en (as in embolden, enliven).
3 (added to verbs) in; into; on : ensnare.
• as an intensifier : entangle.
ORIGIN from French, from Latin in-. See also in- 2 , a commonly found by-form.
en- 2 (also em-)
within; inside : encyst | endemic | embolism | empyema.
ORIGIN from Greek. --Oxford American Dictionary