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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).
Together; joint; jointly; mutually: coaptation.
Subordinate or auxiliary: coenzyme.
To the same extent or degree: codominant.