The Collaborative International Dictionary of English v.0.48:

Communist \Com"mu*nist\, n. [F. communiste.]
   1. An advocate for the theory or practice of communism.
      [1913 Webster]

   2. A supporter of the commune of Paris.
      [1913 Webster]

WordNet (r) 3.0 (2006):

communist
    adj 1: relating to or marked by communism; "Communist Party";
           "communist governments"; "communistic propaganda" [syn:
           communist, communistic]
    n 1: a member of the communist party
    2: a socialist who advocates communism [syn: communist,
       commie]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "communist":
   associated, coacting, coactive, coadjutant, coadjuvant,
   coefficient, collaborative, collective, collectivist,
   collectivistic, collusive, combined, commensal, common, communal,
   communalist, communalistic, communistic, communitarian, commutual,
   concerted, concordant, concurrent, concurring, conjoint, conniving,
   cooperant, cooperating, cooperative, ecumenic, fellow, general,
   harmonious, harmonized, in common, joint, mutual, noncompetitive,
   popular, public, reciprocal, social, socialistic, societal,
   symbiotic, synergetic, synergic, synergistic, uncompetitive



Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "Communist":
   Bolshevik, Bolshevist, Bolshie, Carbonarist, Carbonaro, Castroist,
   Castroite, Charley, Communist sympathizer, Cong, Fenian, Guevarist,
   Jacobin, Leninist, Maoist, Marxist, Marxist-Leninist, Mau-Mau,
   Puritan, Red, Red Republican, Roundhead, Sinn Feiner, Stalinist,
   Titoist, Trotskyist, Trotskyite, VC, Vietcong, Yankee,
   Yankee Doodle, anarch, anarchist, avowed Communist, bolshie,
   bonnet rouge, commie, criminal syndicalist, fellow traveler, rebel,
   red, revisionist, revolutionary, revolutionary junta, revolutioner,
   revolutionist, revolutionizer, sans-culotte, sans-culottist,
   subversive, syndicalist, terrorist