The Collaborative International Dictionary of English v.0.48:

Cooperate \Co*["o]p"er*ate\, v. i. [imp. & p. p. Cooperated;
   p. pr. & vb. n. Cooperating.] [L. cooperatus, p. p. of
   cooperari to cooperate; co + operari to work, opus work. See
   Operate.]
   To act or operate jointly with another or others; to concur
   in action, effort, or effect.
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         Whate'er cooperates to the common mirth. --Crashaw.
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