The Collaborative International Dictionary of English v.0.48:

Comedian \Co*me"di*an\, n. [Cf. F. com['e]dien.]
   1. An actor or player in comedy. "The famous comedian,
      Roscius." --Middleton.
      [1913 Webster]

   2. A writer of comedy. --Milton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

comedian
    n 1: a professional performer who tells jokes and performs
         comical acts [syn: comedian, comic]
    2: an actor in a comedy

Moby Thesaurus II by Grady Ward, 1.0:

65 Moby Thesaurus words for "comedian":
   banana, buffoon, burlesquer, card, caricaturist, choreographer,
   clown, comedienne, comic, cutup, dramatist, dramatizer, dramaturge,
   droll, epigrammatist, farcer, farceur, farceuse, farcist, fool,
   funnyman, gag writer, gagman, gagster, genteel comedian,
   hoke comic, humorist, ironist, jester, joke writer, joker,
   jokesmith, jokester, lampooner, librettist, light comedian,
   low comedian, madcap, melodramatist, mimographer, monodramatist,
   parodist, play doctor, play fixer, playwright, playwriter,
   prankster, punner, punster, quipster, reparteeist, satirist,
   scenario writer, scenarioist, scenarist, scriptwriter,
   slapstick comedian, stand-up comic, tragedian, wag, wagwit,
   wisecracker, wit, witling, zany