'Cooperator' definitions:

Definition of 'cooperator'

From: WordNet
noun
An associate in an activity or endeavor or sphere of common interest; "the musician and the librettist were collaborators"; "sexual partners" [syn: collaborator, cooperator, partner, pardner]

Definition of 'Cooperator'

From: GCIDE
  • Cooperator \Co*["o]p"er*a`tor\, n. [L.: cf. F. coop['e]rateur.] One who labors jointly with others to promote the same end. "Cooperators with the truth." --Boyle. [1913 Webster]