The Collaborative International Dictionary of English v.0.48:

Restraint \Re*straint"\, n. [OF. restraincte, fr. restrainct, F.
   restreint, p. p. of restraindre, restrendre. See Restrain.]
   1. The act or process of restraining, or of holding back or
      hindering from motion or action, in any manner; hindrance
      of the will, or of any action, physical or mental.
      [1913 Webster]

            No man was altogether above the restrains of law,
            and no man altogether below its protection.
                                                  --Macaulay.
      [1913 Webster]

   2. The state of being restrained.
      [1913 Webster]

   3. That which restrains, as a law, a prohibition, or the
      like; limitation; restriction.
      [1913 Webster]

            For one restraint, lords of the world besides.
                                                  --Milton.
      [1913 Webster]

   Syn: Repression; hindrance; check; stop; curb;?oercion;
        confinement; limitation; restriction.
        [1913 Webster]

WordNet (r) 3.0 (2006):

restraint
    n 1: the act of controlling by restraining someone or something;
         "the unlawful restraint of trade"
    2: discipline in personal and social activities; "he was a model
       of polite restraint"; "she never lost control of herself"
       [syn: restraint, control] [ant: unrestraint]
    3: the state of being physically constrained; "dogs should be
       kept under restraint" [syn: constraint, restraint]
    4: a rule or condition that limits freedom; "legal restraints";
       "restraints imposed on imports"
    5: lack of ornamentation; "the room was simply decorated with
       great restraint" [syn: chasteness, restraint,
       simplicity, simpleness]
    6: a device that retards something's motion; "the car did not
       have proper restraints fitted" [syn: restraint,
       constraint]

Moby Thesaurus II by Grady Ward, 1.0:

304 Moby Thesaurus words for "restraint":
   Atticism, Oregon boat, abnegation, absolutism, abstinence,
   aloofness, aplomb, appropriateness, arrest, arrestation,
   arrestment, assurance, backwardness, balance, ban, bashfulness,
   bilbo, blankness, block, blockage, blocking, bond, bond service,
   bondage, bonds, bounds, bracelets, bridle, caging, calm, calmness,
   camisole, captivity, censorship, chains, chasteness, chastity,
   check, chilliness, circumscription, clarity, classicalism,
   classicism, clearness, clogging, closing up, closure, coaction,
   coldness, collar, comeliness, composure, compulsion,
   compulsiveness, confidence, confinement, conservatism, constraint,
   constriction, continence, control, cool, coolness, correctness,
   cramp, cuffs, curb, curtailment, debt slavery, delay, delimitation,
   deprivation of freedom, detachment, detainment, detention, dignity,
   directness, discipline, discreetness, discretion, discrimination,
   disenfranchisement, disfranchisement, dispassion, distance,
   distinction, domination, ease, elegance, elegancy, embargo,
   enforcement, enslavement, enthrallment, equability, equanimity,
   equilibrium, evenness, expressionlessness, felicitousness,
   felicity, fetter, fetters, feudalism, feudality, finish,
   fittingness, fixation, flow, flowing periods, fluency,
   foot-dragging, forbearance, forcing, frigidity, frostiness,
   frugality, gag, gentleness, golden mean, good taste, grace,
   gracefulness, gracility, guardedness, gyves, halter, hamper,
   hampering, handcuffs, happy medium, helotism, helotry, hindering,
   hindrance, hobbles, holdback, holdup, hopples, iciness,
   impartiality, impassiveness, impassivity, impediment,
   impersonality, impoundment, inaccessibility, indentureship,
   independence, inevitability, inhibition, interdict, interdiction,
   interference, interruption, introversion, irons, irresistibility,
   judiciousness, juste-milieu, leading strings, leash, lenity, let,
   level head, levelheadedness, limit, limitation, limpidity, lockup,
   lucidity, manacle, meden agan, middle way, mildness, moderateness,
   moderation, moderationism, modesty, muzzle, naturalness, neatness,
   necessity, negativism, neutrality, nonviolence, nothing in excess,
   nuisance value, obligation, obligement, obstruction,
   obstructionism, occlusion, opposition, pacifism, pellucidity,
   penning, peonage, perspicuity, pillory, plainness, poise, polish,
   possession, presence of mind, propriety, proscription, prudence,
   psychological block, purity, quietness, refinement, rein, reins,
   remoteness, renouncement, renunciation, repose, repression,
   reserve, reservedness, resistance, restrainedness, restraints,
   restriction, retardation, retardment, reticence, reticency,
   retirement, retiring disposition, seemliness, self-abnegation,
   self-assurance, self-command, self-confidence, self-conquest,
   self-control, self-denial, self-discipline, self-government,
   self-mastery, self-possession, self-restraint, serenity, serfdom,
   serfhood, servility, servitude, setback, shackle, shackles,
   simplicity, slavery, smoothness, soberness, sobriety, sophrosyne,
   squeeze, stability, standoffishness, steadiness, stocks,
   straightforwardness, straightjacket, strait-waistcoat,
   straitjacket, stranglehold, stricture, subduedness, subjection,
   subjugation, suppression, taboo, taste, tastefulness, temperance,
   temperateness, terseness, tether, thrall, thralldom, trammel,
   trammels, tranquillity, tyranny, unaffability, unaffectedness,
   unapproachability, uncongeniality, undemonstrativeness,
   understatement, unexcessiveness, unexpansiveness, unextravagance,
   unextremeness, unobtrusiveness, vassalage, via media, villenage,
   well-regulated mind, withdrawal, withdrawnness, yoke