The Collaborative International Dictionary of English v.0.48:

Dissident \Dis"si*dent\, n. (Eccl.)
   One who disagrees or dissents; one who separates from the
   established religion.
   [1913 Webster]

         The dissident, habituated and taught to think of his
         dissidenc? as a laudable and necessary opposition to
         ecclesiastical usurpation.               --I. Taylor.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Dissident \Dis"si*dent\, a. [L. dissidens, -entis, p. pr. of
   dissidere to sit apart, to disagree; dis- + sedere to sit:
   cf. F. dissident. See Sit.]
   No agreeing; dissenting; discordant; different.
   [1913 Webster]

         Our life and manners be dissident from theirs.
                                                  --Robynson
                                                  (More's
                                                  Utopia).
   [1913 Webster]

WordNet (r) 3.0 (2006):

dissident
    adj 1: characterized by departure from accepted beliefs or
           standards [syn: dissident, heretical, heterodox]
    2: disagreeing, especially with a majority [syn: dissentient,
       dissenting(a), dissident]
    n 1: a person who dissents from some established policy [syn:
         dissenter, dissident, protester, objector,
         contestant]

Moby Thesaurus II by Grady Ward, 1.0:

118 Moby Thesaurus words for "dissident":
   alienated, antagonistic, antiestablishment, antipathetic, apostate,
   at cross-purposes, at loggerheads, at odds, at odds with,
   at variance, at variance with, at war, bitter-ender, brawler,
   breakaway, clashing, colliding, conflicting, contentious,
   contradicting, contradictory, contrary, counter-culture,
   counteractant, counteracting, counteractive, countervailing,
   counterworking, cranky, cross, crotchety, defendant, demurrer,
   deviant, diehard, differing, disaccordant, disagreeable,
   disagreeing, discordant, discrepant, disharmonious,
   disproportionate, disputant, dissenter, dissentient, dissenting,
   dissonant, divergent, grating, heretic, heterodox, hostile,
   immiscible, in opposition, inaccordant, incompatible, inharmonious,
   inimical, intransigent, irreconcilable, jangling, jarring,
   last-ditcher, litigant, misbeliever, naysayer, negative,
   negativist, nonconformable, nonconforming, nonconformist,
   noncooperator, nonobservant, objector, obstructionist, obstructive,
   opinionist, opposer, opposing, opposition voice, oppositional,
   oppositionist, oppugnant, out of accord, out of whack, perverse,
   plaintiff, protestant, protester, protestor, quarreler,
   reactionary, rebel, recalcitrant, recusant, refractory, renitent,
   repugnant, resistant, resister, revolutionary, schismatic,
   scrapper, sectarian, sectary, separatist, unadaptable,
   unadjustable, uncompliant, unconforming, uncongenial, underground,
   unharmonious, unorthodox, unsubmissive, variant, wrangler