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com-

  1. a prefix meaning “with,” “together,” “in association,” and (with intensive force) “completely,” occurring in loanwords from Latin (commit): used in the formation of compound words before b, p, m: combine; compare; commingle.
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Also co-, col-, con-, cor-.

Origin of com-

< Latin, variant of preposition cum with
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for com-

com-

con-

prefix
  1. together; with; jointlycommingle
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Word Origin for com-

from Latin com-; related to cum with. In compound words of Latin origin, com- becomes col- and cor- before l and r, co- before gn, h, and most vowels, and con- before consonants other than b, p, and m. Although its sense in compounds of Latin derivation is often obscured, it means: together, with, etc (combine, compile) ; similar (conform); extremely, completely (consecrate)
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for com-

word-forming element usually meaning "with, together," from Latin com, archaic form of classical Latin cum "together, together with, in combination," from PIE *kom- "beside, near, by, with" (cf. Old English ge-, German ge-). The prefix in Latin sometimes was used as an intensive.

Before vowels and aspirates, reduced to co-; before -g-, assimilated to cog- or con-; before -l-, assimilated to col-; before -r-, assimilated to cor-; before -c-, -d-, -j-, -n-, -q-, -s-, -t-, -v- assimilated to con-.

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Online Etymology Dictionary, © 2010 Douglas Harper

com- in Medicine

com-

pref.
  1. Together; with; joint; jointly:commensalism.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.