The Collaborative International Dictionary of English v.0.48:

Dissent \Dis*sent"\, n.
   1. The act of dissenting; difference of opinion; refusal to
      adopt something proposed; nonagreement, nonconcurrence, or
      disagreement.
      [1913 Webster]

            The dissent of no small number [of peers] is
            frequently recorded.                  --Hallam.
      [1913 Webster]

   2. (Eccl.) Separation from an established church, especially
      that of England; nonconformity.
      [1913 Webster]

            It is the dissidence of dissent and the
            protestantism of the Protestant religion. --Burke.
      [1913 Webster]

   3. Contrariety of nature; diversity in quality. [Obs.]
      [1913 Webster]

            The dissent of the metals.            --Bacon.

   Syn: Disagreement; variance; difference; nonconcurrence;
        nonconformity.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Dissent \Dis*sent"\, v. i. [imp. & p. p. Dissented; p. pr. &
   vb. n. Dissenting.] [L. dissentire, dissentum; dis- +
   sentire to feel, think. See Sense.]
   1. To differ in opinion; to be of unlike or contrary
      sentiment; to disagree; -- followed by from.
      [1913 Webster]

            The bill passed . . . without a dissenting voice.
                                                  --Hallam.
      [1913 Webster]

            Opinions in which multitudes of men dissent from us.
                                                  --Addison.
      [1913 Webster]

   2. (Eccl.) To differ from an established church in regard to
      doctrines, rites, or government.
      [1913 Webster]

   3. To differ; to be of a contrary nature. --Hooker.
      [1913 Webster]

WordNet (r) 3.0 (2006):

dissent
    n 1: (law) the difference of one judge's opinion from that of
         the majority; "he expressed his dissent in a contrary
         opinion"
    2: a difference of opinion
    3: the act of protesting; a public (often organized)
       manifestation of dissent [syn: protest, objection,
       dissent]
    v 1: withhold assent; "Several Republicans dissented" [ant:
         accede, acquiesce, assent]
    2: express opposition through action or words; "dissent to the
       laws of the country" [syn: protest, resist, dissent]
    3: be of different opinions; "I beg to differ!"; "She disagrees
       with her husband on many questions" [syn: disagree,
       differ, dissent, take issue] [ant: agree, concord,
       concur, hold]

Moby Thesaurus II by Grady Ward, 1.0:

386 Moby Thesaurus words for "dissent":
   Evangelicalism, Protestantism, Reform, Zwinglianism, abnegation,
   aggressiveness, agree to differ, agree to disagree, antagonism,
   antipathy, apostasy, argumentation, averseness, aversion, backlash,
   backwardness, balk, ban, be at cross-purposes, be at variance,
   be in dissent, be unmoved, be unwilling, beef, beefing, beg off,
   beg to differ, bellicosity, belligerence, bellyache, bellyaching,
   bickering, bitch, bitching, blackball, blackballing, boggle, break,
   break bounds, break off, break step, break up,
   categorically reject, challenge, clash, clashing, collide,
   collision, combative reaction, combativeness, complain,
   complain loudly, complaining, complaint, conflict, confront,
   confutation, contend with, contention, contentiousness, contradict,
   contradiction, contraposition, contrariety, contrast, controversy,
   counter, counteraction, counterposition, counterworking,
   crankiness, crotchetiness, cursoriness, declension, declination,
   declinature, decline, decline to accept, declining, defiance,
   demur, denial, departure, deprivation, destructive criticism,
   deviation, differ, difference, differentiate, dim view, disaccord,
   disaccordance, disagree, disagree with, disagreement, disallow,
   disallowance, disappointment, disapprobation, disapproval,
   disapprove, disapprove of, disclaim, disclaimer, disclamation,
   disconformity, discongruity, discontent, discontentedness,
   discontentment, discord, discord with, discordance, discordancy,
   discrepancy, discreteness, disenchantment, disesteem, disfavor,
   disgruntlement, disharmony, disillusion, disillusionment,
   disinclination, disobedience, disparity, displeasure, dispute,
   disrelish, disrespect, dissatisfaction, dissension, dissent from,
   dissentience, dissidence, dissimilarity, dissonance, distaste,
   distinction, distinctness, disunify, disunion, disunity,
   divaricate, diverge, divergence, divergency, diversify, diversity,
   divide, divide on, drop out, exclude, exclusion, face down,
   face out, face up to, faction, factiousness, far cry, faultfinding,
   flak, foot-dragging, fractiousness, friction, front, frown at,
   frown down, frown upon, grievance, grimace at, gripe, griping,
   groan, groaning, grouse, grousing, grudging consent, grudgingness,
   grumbling, heterodoxy, heterogeneity, hold out against,
   holding back, holler, howl, inaccordance, incompatibility,
   incongruity, inconsistency, inconsonance, indignation,
   indisposedness, indisposition, indocility, inequality, infighting,
   inharmoniousness, inharmony, interference, intractableness,
   irascibility, irreconcilability, irritability, jangle, jar,
   jarring, jostle, kick, kick against, kicking, lack of enthusiasm,
   lack of zeal, litigiousness, look askance at, look black upon,
   low estimation, low opinion, make a stand, make waves,
   meet head-on, misbelief, mismatch, mismate, mixture, murmuring,
   mutinousness, nay, negate, negation, negative, negative answer,
   negativism, new theology, nix, no, nolition, nonacceptance,
   nonagreement, noncompliance, nonconcurrence, nonconform,
   nonconformance, nonconformism, nonconformity, nonconsent,
   noncooperation, nonobservance, not agree, not approve, not buy,
   not comply, not conform, not consent, not go for, not hear of,
   not hold with, not think of, object, object to, objection,
   obstinacy, odds, offer resistance, oppose, opposition, opposure,
   oppugnance, oppugnancy, opt out, originality, ostracism, ostracize,
   otherness, partisan spirit, partisanship, passive resistance,
   peeve, peevishness, perfunctoriness, perverseness, pet peeve,
   petulance, protest, pugnacity, quarrelsomeness, querulousness,
   reaction, rebuff, recalcitrance, recalcitrancy, recalcitrate,
   recalcitration, recantation, recoil, recusance, recusancy,
   refractoriness, refusal, refuse, refuse consent, reject, rejection,
   relieve, reluct, reluctance, remonstrance, remonstrate, renitence,
   renitency, repellence, repellency, repercussion, repudiate,
   repudiation, repugnance, repulse, repulsion, resist entreaty,
   resist persuasion, resistance, retention, revolt, rock the boat,
   say nay, say no, say no to, schism, scolding, secede, separateness,
   show fight, shrewishness, shy, slowness, sniping, squawk,
   squawking, stand, stand aloof, stand at bay, stand up against,
   stand up to, stickle, strife, strive against, stubbornness, sulk,
   sulkiness, sulks, sullenness, swimming upstream, take exception,
   take exception to, take issue, think ill of, think little of,
   thumb down, thumbs-down, turn down, turndown, unconformity,
   uncooperativeness, unenthusiasm, unhappiness, unharmoniousness,
   unlikeness, unorthodoxy, unwillingness, variance, variate,
   variation, variegate, variegation, variety, vary,
   view with disfavor, vote nay, vote negatively, whining, withdraw,
   withhold assent, withholding, withstand, withstanding, yapping



Bouvier's Law Dictionary, Revised 6th Ed (1856):

DISSENT, contracts. A disagreement to something which has been done. It is
express or implied.
     2. The law presumes that every person to whom a conveyance has been
made has given his assent to it, because it is supposed to be for his
benefit. To rebut the presumption, his dissent must be expressed. Vide 4
Mason, R. 206; 11 Wheat. R. 78; 1 Binn. R. 502; 2 Binn. R. 174; 6 Binn. R.
338; 12 Mass. R. 456; 17 Mass. R. 552; 3 John. Ch. R. 261; 4 John. Ch. R.
136, 529; and dissent, and the authorities there cited.