Source : Webster's Revised Unabridged Dictionary (1913)

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.

         Long imprisonment and hard constraint.   --Spenser.

         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.

Source : WordNet®

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

Source : Free On-Line Dictionary of Computing

constraint
     
         A {Boolean} {relation}, often an
        equality or {ineqality} relation, between the values of one or
        more mathematical variables (often two).  E.g. x>3 is a
        constraint on x.  {constraint satisfaction} attempts to assign
        values to variables so that all constraints are true.
     
        {Usenet} newsgroup: {news:comp.constraints}.  {FAQ
        (http://www.cs.unh.edu/ccc/archive/)}.
     
        (2002-06-08)