The Collaborative International Dictionary of English v.0.48:

Conservatism \Con*serv"a*tism\, n. [For conservatism.]
   The disposition and tendency to preserve what is established;
   opposition to change; the habit of mind; or conduct, of a
   conservative.
   [1913 Webster]

WordNet (r) 3.0 (2006):

conservatism
    n 1: a political or theological orientation advocating the
         preservation of the best in society and opposing radical
         changes [syn: conservatism, conservativism]

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "conservatism":
   abnegation, abstinence, backwardness, calm, calmness,
   conservativeness, constraint, continence, control, cool,
   dispassion, evenness, fogyism, gentleness, golden mean,
   happy medium, impartiality, judiciousness, juste-milieu,
   laissez-faireism, lenity, meden agan, middle way, mildness,
   moderateness, moderation, moderationism, neutrality, nonviolence,
   nothing in excess, old school tie, old-fashionedness, pacifism,
   political conservatism, prudence, repose, resistance to change,
   restraint, rightism, self-abnegation, self-control, self-denial,
   self-restraint, serenity, sobriety, stability, standpattism,
   steadiness, temperance, temperateness, tranquillity,
   ultraconservatism, unexcessiveness, unextravagance, unextremeness,
   unprogressiveness, via media