variant of en-1 before b, p, and sometimes m: embalm.
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from French assimilation of en- to following labial (see en- (1)). Also a prefix used to form verbs from adjectives and nouns.
representing Latin ex- assimilated to following -m- (see ex-).
Online Etymology Dictionary, © 2010 Douglas Harper
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.