from The American Heritage® Dictionary of the English Language, 4th Edition

  • Together; joint; jointly; mutually: coeducation.
  • Partner or associate in an activity: coauthor; cofounder.
  • Subordinate or assistant: copilot.
  • To the same extent or degree: coextensive.
  • Complement of an angle: cotangent.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • together; mutually; jointly
  • partner or subordinate in an activity
  • to the same degree
  • of the opposite, of the counterpart

from the GNU version of the Collaborative International Dictionary of English

  • A form of the prefix com-, signifying with, together, in conjunction, joint. It is used before vowels and some consonants. See com-.


Middle English, from Latin, variant of com-, com-.
(American Heritage® Dictionary of the English Language, Fourth Edition)
From the Latin prefix co-. (Wiktionary)



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