The Collaborative International Dictionary of English v.0.48:

Marxist \Marx"ist\, prop. n.
   One who believes in the theories of Karl Marx.
   [PJC]

The Collaborative International Dictionary of English v.0.48:

Marxist \Marx"ist\, prop. a.
   Of or pertaining to Marx or Marxism.
   [PJC]

WordNet (r) 3.0 (2006):

Marxist
    adj 1: following the ideas of Marx and Engels
    n 1: an advocate of Marxism
    2: emotionally charged terms used to refer to extreme radicals
       or revolutionaries [syn: Bolshevik, Marxist, red,
       bolshie, bolshy]

Moby Thesaurus II by Grady Ward, 1.0:

88 Moby Thesaurus words for "Marxist":
   Bolshevik, Bolshevist, Bolshie, Carbonarist, Carbonaro, Castroist,
   Castroite, Charley, Communist, Communist sympathizer, Cong, Fabian,
   Fabian socialist, Fenian, Fourierist, Guevarist, Jacobin,
   Jacobinic, Leninist, Maoist, Marxian, Marxist-Leninist, Mau-Mau,
   Owenite, Puritan, Red, Red Republican, Roundhead, Saint-Simonian,
   Sinn Feiner, Stalinist, Titoist, Trotskyist, Trotskyite, VC,
   Vietcong, Yankee, Yankee Doodle, agin the government, anarch,
   anarchic, anarchist, atomistic, avowed Communist, bolshie,
   bonnet rouge, collectivist, commie, commonsense,
   commonsense philosopher, communistic, criminal syndicalist,
   dialectical materialist, epistemological realist, fellow traveler,
   hylomorphous, hylotheistic, materialist, materialistic, mechanist,
   mechanistic, natural realist, naturalist, naturalistic,
   phalansterian, physicist, positivist, positivistic, realist,
   realistic, rebel, red, revisionist, revolutionary,
   revolutionary junta, revolutioner, revolutionist, revolutionizer,
   sans-culotte, sans-culottic, sans-culottish, sans-culottist,
   socialist, state socialist, subversive, syndicalist, terrorist,
   utopian socialist