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co-

1.
variant of com- before a vowel, h, and gn: coadjutor; cohabit; cognate . The prefix co-, now productively forms new words from bases beginning with any sound (co-conspirator; co-manage; coseismic), sometimes with the derived sense “auxiliary, subsidiary” (coenzyme; copilot), and, in mathematics and astronomy, with the sense “complement” (codeclination).
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Based on the Random House Dictionary, © Random House, Inc. 2014.
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British Dictionary definitions for co-

co-

prefix
1.
together; joint or jointly; mutual or mutually: coproduction
2.
indicating partnership or equality: cofounder, copilot
3.
to the same or a similar degree: coextend
4.
(in mathematics and astronomy) of the complement of an angle: cosecant, codeclination
Word Origin
from Latin, reduced form of com-
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
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Word Origin and History for co-

in Latin, the form of com- in compounds with stems beginning in vowels and h- and gn- (see com-). Taken in English from 17c. as a living prefix meaning "together, mutually, in common," and used promiscuously with native words and Latin-derived words not beginning with vowels, sometimes even with words already having it (e.g. co-conspiritor).

Online Etymology Dictionary, © 2010 Douglas Harper
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co- in Medicine

co- pref.

  1. Together; joint; jointly; mutually: coaptation.

  2. Subordinate or auxiliary: coenzyme.

  3. To the same extent or degree: codominant.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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