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

The Free On-line Dictionary of Computing (19 January 2023):

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)