WordNet (r) 3.0 (2006):

straight man
    n 1: a performer who acts as stooge to a comedian [syn:
         straight man, second banana]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "straight man":
   Roscius, actor, actress, antagonist, bad guy, barnstormer,
   character, character actor, character man, character woman,
   child actor, diseur, diseuse, dramatizer, feeder, foil, heavy,
   histrio, histrion, ingenue, juvenile, matinee idol, mime, mimer,
   mimic, monologist, mummer, pantomime, pantomimist, playactor,
   player, protean actor, reciter, soubrette, stage performer,
   stage player, stooge, stroller, strolling player, theatrical,
   thespian, trouper, utility man, villain