The Collaborative International Dictionary of English v.0.48:

collaborate \col*lab"o*rate\, v. i.
   1. to work together with another toward a common goal,
      especially in an intellectual endeavor; as, four chemists
      collaborated on the synthesis of the compound; three
      authors collaborated in writing the book.
      [PJC]

   2. to willingly cooperate with an enemy, especially an enemy
      nation occupying one's own country.
      [PJC]

WordNet (r) 3.0 (2006):

collaborate
    v 1: work together on a common enterprise of project; "The
         soprano and the pianist did not get together very well";
         "We joined forces with another research group" [syn:
         collaborate, join forces, cooperate, get together]
    2: cooperate as a traitor; "he collaborated with the Nazis when
       they occupied Paris"