The Collaborative International Dictionary of English v.0.48:

Closure \Clo"sure\ (kl[=o]"zh[-u]r; 135), n. [Of. closure, L.
   clausura, fr. clauedere to shut. See Close, v. t.]
   1. The act of shutting; a closing; as, the closure of a
      chink.
      [1913 Webster]

   2. That which closes or shuts; that by which separate parts
      are fastened or closed.
      [1913 Webster]

            Without a seal, wafer, or any closure whatever.
                                                  --Pope.
      [1913 Webster]

   3. That which incloses or confines; an inclosure.
      [1913 Webster]

            O thou bloody prison . . .
            Within the guilty closure of thy walls
            Richard the Second here was hacked to death. --Shak.
      [1913 Webster]

   4. A conclusion; an end. [Obs.] --Shak.
      [1913 Webster]

   5. (Parliamentary Practice) A method of putting an end to
      debate and securing an immediate vote upon a measure
      before a legislative body. It is similar in effect to the
      previous question. It was first introduced into the
      British House of Commons in 1882. The French word
      cl[^o]ture was originally applied to this proceeding.
      [1913 Webster]

   6. (Math.) the property of being mathematically closed under
      some operation; -- said of sets.
      [PJC]

   7. (Math.) the intersection of all closed sets containing the
      given set.
      [PJC]

   8. (Psychol.) achievement of a sense of completeness and
      release from tension due to uncertainty; as, the closure
      afforded by the funeral of a loved one; also, the sense of
      completion thus achieved.
      [PJC]

WordNet (r) 3.0 (2006):

closure
    n 1: approaching a particular destination; a coming closer; a
         narrowing of a gap; "the ship's rapid rate of closing gave
         them little time to avoid a collision" [syn: closing,
         closure]
    2: a rule for limiting or ending debate in a deliberative body
       [syn: closure, cloture, gag rule, gag law]
    3: a Gestalt principle of organization holding that there is an
       innate tendency to perceive incomplete objects as complete
       and to close or fill gaps and to perceive asymmetric stimuli
       as symmetric [syn: closure, law of closure]
    4: something settled or resolved; the outcome of decision
       making; "they finally reached a settlement with the union";
       "they never did achieve a final resolution of their
       differences"; "he needed to grieve before he could achieve a
       sense of closure" [syn: settlement, resolution,
       closure]
    5: an obstruction in a pipe or tube; "we had to call a plumber
       to clear out the blockage in the drainpipe" [syn: blockage,
       block, closure, occlusion, stop, stoppage]
    6: the act of blocking [syn: blockage, closure, occlusion]
    7: termination of operations; "they regretted the closure of the
       day care center" [syn: closure, closedown, closing,
       shutdown]
    v 1: terminate debate by calling for a vote; "debate was
         closured"; "cloture the discussion" [syn: closure,
         cloture]

Moby Thesaurus II by Grady Ward, 1.0:

103 Moby Thesaurus words for "closure":
   accomplishment, ankle, arrest, arrestation, arrestment,
   articulation, blockage, blocking, boundary, butt, cease, cervix,
   cessation, check, clinch, clogging, close, closing, closing up,
   completion, conclusion, connecting link, connecting rod,
   connection, constriction, consummation, coupling, cramp,
   culmination, delay, desistance, detainment, detention, dovetail,
   elbow, embrace, end, ending, fixation, foot-dragging, fulfillment,
   gliding joint, hampering, hindering, hindrance, hinge,
   hinged joint, hip, holdback, holdup, impediment, inhibition,
   interface, interference, interruption, join, joining, joint,
   juncture, knee, knuckle, let, link, miter, mortise, neck,
   negativism, nuisance value, obstruction, obstructionism, occlusion,
   opposition, perfection, pivot, pivot joint, rabbet, realization,
   repression, resistance, restraint, restriction, retardation,
   retardment, scarf, seam, setback, shoulder, squeeze, stitch, stop,
   stranglehold, stricture, suppression, suture, symphysis,
   termination, tie rod, toggle, toggle joint, topping-off, union,
   weld, wrist



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

closure
downward closed
upward closure

   1.  In a reduction system, a closure is a data
   structure that holds an expression and an environment of
   variable bindings in which that expression is to be evaluated.
   The variables may be local or global.  Closures are used to
   represent unevaluated expressions when implementing
   functional programming languages with lazy evaluation.  In
   a real implementation, both expression and environment are
   represented by pointers.

   A suspension is a closure which includes a flag to say
   whether or not it has been evaluated.  The term "thunk" has
   come to be synonymous with "closure" but originated outside
   functional programming.

   2.  In domain theory, given a partially ordered
   set, D and a subset, X of D, the upward closure of X in D is
   the union over all x in X of the sets of all d in D such that
   x <= d.  Thus the upward closure of X in D contains the
   elements of X and any greater element of D.  A set is "upward
   closed" if it is the same as its upward closure, i.e. any d
   greater than an element is also an element.  The downward
   closure (or "left closure") is similar but with d <= x.  A
   downward closed set is one for which any d less than an
   element is also an element.

   ("<=" is written in LaTeX as \subseteq and the upward
   closure of X in D is written \uparrow_\D X).

   (1994-12-16)