The Collaborative International Dictionary of English v.0.48:

Role \Role\, Role \R[^o]le\, n. [F. See Roll.]
   A part, or character, performed by an actor in a drama;
   hence, a part of function taken or assumed by any one; as, he
   has now taken the role of philanthropist.
   [1913 Webster]

   Title role, the part, or character, which gives the title
      to a play, as the part of Hamlet in the play of that name.
      [1913 Webster]

WordNet (r) 3.0 (2006):

role
    n 1: the actions and activities assigned to or required or
         expected of a person or group; "the function of a teacher";
         "the government must do its part"; "play its role" [syn:
         function, office, part, role]
    2: an actor's portrayal of someone in a play; "she played the
       part of Desdemona" [syn: character, role, theatrical
       role, part, persona]
    3: what something is used for; "the function of an auger is to
       bore holes"; "ballet is beautiful but what use is it?" [syn:
       function, purpose, role, use]
    4: normal or customary activity of a person in a particular
       social setting; "what is your role on the team?"

Moby Thesaurus II by Grady Ward, 1.0:

59 Moby Thesaurus words for "role":
   actor, antagonist, antihero, bit, bit part, capacity, cast,
   character, condition, cue, duty, end use, fat part, feeder,
   function, heavy, hero, heroine, immediate purpose, impersonation,
   ingenue, job, lead, lead role, leading lady, leading man,
   leading woman, lines, office, operation, operational purpose, part,
   person, personage, piece, place, position, post, protagonist,
   province, purpose, quality, relation, responsibility, side,
   situation, soubrette, status, straight part, supporting character,
   supporting role, task, title role, ultimate purpose, use, villain,
   walk-on, walking part, work