Source : Webster's Revised Unabridged Dictionary (1913)

Collaborator \Col*lab"o*ra`tor\, n. [L. collaborare to labor
   together; col- + laborare to labor: cf. F. collaborateur.]
   An associate in labor, especially in literary or scientific
   labor.

Source : WordNet®

collaborator
     n 1: someone who assists in a plot [syn: {confederate}, {henchman},
           {partner in crime}]
     2: someone who collaborates with an enemy occupying force [syn:
         {collaborationist}, {quisling}]
     3: an associate who works with others toward a common goal;
        "partners in crime" [syn: {cooperator}, {partner}, {pardner}]