The Collaborative International Dictionary of English v.0.48:

Reinforce \Re`in*force"\ (-f?rs"), v. t.
   See Reenforce, v. t.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Reinforce \Re`in*force"\, n.
   See Reenforce, n.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Reenforce \Re`en*force"\, Re-enforce \Re`-en*force"\(-f?rs"), v.
   t. [Pref. re- + enforce: cf. F. renforcer.]
   1. To strengthen with new force, assistance, material, or
      support; as, to reenforce an argument; to reenforce a
      garment; especially, to strengthen with additional troops,
      as an army or a fort, or with additional ships, as a
      fleet. [Written also reinforce.]
      [1913 Webster]

   2. (Psychology) To increase the likelihood that (a specific
      behavior) will be repeated by giving a reward or
      punishment to a person or animal; as, to reenforce the
      students' willingness to study by giving awards for good
      grades.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Reenforce \Re`en*force"\, n. [See Reenforce, v., and cf.
   Ranforce, Reinforce.]
   Something which reenforces or strengthens. Specifically:
   (a) That part of a cannon near the breech which is thicker
       than the rest of the piece, so as better to resist the
       force of the exploding powder. See Illust. of Cannon.
   (b) An additional thickness of canvas, cloth, or the like,
       around an eyelet, buttonhole, etc. [Written also
       reinforce.]
       [1913 Webster]

WordNet (r) 3.0 (2006):

reinforce
    v 1: make stronger; "he reinforced the concrete" [syn:
         reinforce, reenforce]
    2: strengthen and support with rewards; "Let's reinforce good
       behavior" [syn: reinforce, reward]

Moby Thesaurus II by Grady Ward, 1.0:

119 Moby Thesaurus words for "reinforce":
   accelerate, add to, affirm, afford support, aggravate, attest,
   augment, authenticate, back, back up, bear, bear out, bear up,
   beef up, blow up, bolster, bolster up, brace, brace up, buoy up,
   buttress, carry, case harden, certify, circumstantiate, complicate,
   concentrate, condense, confirm, consolidate, corroborate, cradle,
   crutch, cushion, deepen, document, double, energize, enhance,
   enlarge, exacerbate, exaggerate, finance, fortify, fund, gird,
   give support, harden, heat up, heighten, hold, hold up, hop up,
   hot up, increase, intensify, invigorate, jazz up, keep,
   keep afloat, keep up, key up, lend support, magnify, mainstay,
   maintain, make complex, multiply, nerve, pillar, pillow, probate,
   prop, prop up, prove, ramify, ratify, recruit, redouble, refresh,
   reinvigorate, restrengthen, rigidify, screw up, sharpen, shore,
   shore up, shoulder, soup up, stay, steel, step up, stiffen,
   strengthen, subsidize, substantiate, subvention, subventionize,
   supplement, support, sustain, temper, tense, tighten, toughen,
   trice up, triple, underbrace, undergird, underlie, underpin,
   underset, upbear, uphold, upkeep, validate, verify, warrant,
   whet