The Collaborative International Dictionary of English v.0.48:

Constraint \Con*straint"\, n. [OF. constrainte, F. constrainte.]
   The act of constraining, or the state of being constrained;
   that which compels to, or restrains from, action; compulsion;
   restraint; necessity.
   [1913 Webster]

         Long imprisonment and hard constraint.   --Spenser.
   [1913 Webster]

         Not by constraint, but by my choice, I came. --Dryden.

   Syn: Compulsion; violence; necessity; urgency.

   Usage: Constraint, Compulsion. Constraint implies strong
          binding force; as, the constraint of necessity; the
          constraint of fear. Compulsion implies the exertion of
          some urgent impelling force; as, driven by compulsion.
          The former prevents us from acting agreeably to our
          wishes; the latter forces us to act contrary to our
          will. Compulsion is always produced by some active
          agent; a constraint may be laid upon us by the forms
          of civil society, or by other outward circumstances.
          --Crabb.
          [1913 Webster]

WordNet (r) 3.0 (2006):

constraint
    n 1: the state of being physically constrained; "dogs should be
         kept under restraint" [syn: constraint, restraint]
    2: a device that retards something's motion; "the car did not
       have proper restraints fitted" [syn: restraint,
       constraint]
    3: the act of constraining; the threat or use of force to
       control the thoughts or behavior of others

Moby Thesaurus II by Grady Ward, 1.0:

169 Moby Thesaurus words for "constraint":
   abnegation, abstinence, aloofness, aplomb, arrest, arrestation,
   backwardness, bashfulness, blankness, caging, calm, calmness,
   check, chilliness, circumscription, coaction, coercion, coldness,
   composure, compulsion, compulsiveness, confinement, conservatism,
   continence, control, cool, cooling, cooling down, cooling off,
   coolness, cramp, curb, curtailment, deceleration, denial,
   detachment, discipline, discreetness, discretion, dispassion,
   distance, drive, driving, duress, enforcement, evenness, exigency,
   expressionlessness, forbearance, forcing, frigidity, frostiness,
   frugality, gentleness, goad, golden mean, guardedness,
   happy medium, hindrance, iciness, impartiality, impassiveness,
   impassivity, impelling, impersonality, impoundment, impulse,
   impulsion, inaccessibility, independence, inevitability,
   inhibition, injunction, interdict, introversion, irresistibility,
   judiciousness, juste-milieu, legal restraint, lenity, lockup,
   meden agan, middle way, mildness, moderateness, moderation,
   moderationism, modesty, monopoly, motive, necessity, neutrality,
   nonviolence, nothing in excess, obligation, obligement, pacifism,
   penning, pinch, possession, press, pressure, prohibition,
   protection, protectionism, protective tariff, prudence, push,
   rash impulse, rationing, rein, remoteness, renouncement,
   renunciation, repose, repression, reserve, reservedness, restraint,
   restraint of trade, restriction, retardation, reticence, reticency,
   retirement, retiring disposition, retrenchment, self-abnegation,
   self-command, self-conquest, self-control, self-denial,
   self-discipline, self-government, self-mastery, self-possession,
   self-restraint, serenity, slowing down, soberness, sobriety,
   sophrosyne, spring, spur, stability, standoffishness, steadiness,
   stress, subduedness, suppression, tariff wall, temperance,
   temperateness, thought control, tranquillity, unaffability,
   unapproachability, uncongeniality, undemonstrativeness,
   unexcessiveness, unexpansiveness, unextravagance, unextremeness,
   urge, urgency, via media, violence, withdrawal, withdrawnness



The Free On-line Dictionary of Computing (30 December 2018):

constraint

    A Boolean relation, often an
   equality or ineqality relation, between the values of one or
   more mathematical variables.  E.g. x>3 is a constraint on x.
   The process of constraint satisfaction attempts to assign values
   to variables so that all constraints are true.

   Usenet newsgroup: news:comp.constraints.  FAQ
   (http://cs.unh.edu/ccc/archive/).

   (2002-06-08)


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

CONSTRAINT. In the civil and Scottish law, by this term is understood what,
in the common law, is known by the name of duress.
     2. It is a general rule, that when one is compelled into a contract,
there is no effectual consent, though, ostensibly, there is the form of it.
In such case the contract will be declared void.
     3. The constraint requisite thus to annul a contract, must be a vis aut
me us qui cadet in constantem virum, such as would shake a man of firmness
and resolution. 3 Ersk. 1, Sec. 16; and 4, 1, Sec. 26; 1 Bell's Conn. B. 3,
part 1, o. 1, s. 1, art. 1, page 295.