WordNet (r) 3.0 (2006):

negativism
    n 1: characterized by habitual skepticism and a disagreeable
         tendency to deny or oppose or resist suggestions or
         commands [syn: negativity, negativeness, negativism]
         [ant: positiveness, positivism, positivity]

Moby Thesaurus II by Grady Ward, 1.0:

126 Moby Thesaurus words for "negativism":
   abnegation, alienation, arrest, arrestation, arrestment, autism,
   autistic thinking, avoidance mechanism, blame-shifting, blockage,
   blocking, challenge, check, clogging, closing up, closure,
   combative reaction, compensation, complaint, constriction,
   counteraction, cramp, cynicism, decompensation, defeatism,
   defense mechanism, defiance, delay, demur, dereism,
   dereistic thinking, detainment, detention, dismalness,
   displacement, dispute, dissent, dissentience, dissociation,
   emotional insulation, escape, escape into fantasy,
   escape mechanism, escapism, fantasizing, fantasy, fixation, flight,
   foot-dragging, fractiousness, gloominess, gloomy outlook,
   hampering, hindering, hindrance, holdback, holdup, impediment,
   inhibition, interference, interruption, isolation, let, malism,
   nay, naysaying, negation, negative, negative attitude,
   negativeness, negativity, nihilism, nix, no, noncooperation,
   nuisance value, objection, obstinacy, obstruction, obstructionism,
   occlusion, opposition, overcompensation, passive resistance,
   pessimism, projection, protest, psychotaxis, rationalization,
   reaction, rebuff, recalcitrance, recalcitrancy, recalcitration,
   refractoriness, reluctance, remonstrance, renitence, renitency,
   repellence, repellency, repression, repulse, repulsion, resistance,
   restraint, restriction, retardation, retardment, retreatism,
   revolt, setback, sociological adjustive reactions, squeeze, stand,
   stranglehold, stricture, sublimation, substitution, suppression,
   uncheerfulness, uncooperativeness, wish-fulfillment fantasy,
   wishful thinking, withdrawal, withstanding