prefix (also em- before b, p) forming verbs, = IN-(1):
1 from nouns, meaning 'put into or on' (engulf; entrust; embed).
2 from nouns or adjectives, meaning 'bring into the condition of' (enslave); often with the suffix -en (enlighten).
3 from verbs: a in the sense 'in, into, on' (enfold). b as an intensive (entangle).
Etymology: from or after F en- f. L in-
prefix (also em- before b, p) in, inside (energy; enthusiasm).
Useful english dictionary. 2012.