The Collaborative International Dictionary of English v.0.48:

Repay \Re*pay"\ (r?-p?"), v. t. [imp. & p. p. Repaid (-p?d");
   p. pr. & vb. n. Repaying.] [Pref. re- + pay: cf. F.
   repayer.]
   1. To pay back; to refund; as, to repay money borrowed or
      advanced.
      [1913 Webster]

            If you repay me not on such a day,
            In such a place, such sum or sums.    --Shak.
      [1913 Webster]

   2. To make return or requital for; to recompense; -- in a
      good or bad sense; as, to repay kindness; to repay an
      injury.
      [1913 Webster]

            Benefits which can not be repaid . . . are not
            commonly found to increase affection. --Rambler.
      [1913 Webster]

   3. To pay anew, or a second time, as a debt.
      [1913 Webster]

   Syn: To refund; restore; return; recompense; compensate;
        remunerate; satisfy; reimburse; requite.
        [1913 Webster]

WordNet (r) 3.0 (2006):

repay
    v 1: pay back; "Please refund me my money" [syn: refund,
         return, repay, give back]
    2: make repayment for or return something [syn: requite,
       repay]
    3: act or give recompense in recognition of someone's behavior
       or actions [syn: reward, repay, pay back]
    4: answer back [syn: retort, come back, repay, return,
       riposte, rejoin]

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "repay":
   accord, atone, award, balance, be gainful, be profitable,
   be worthwhile, compensate, cover, do penance, expiate, fill up,
   get satisfaction, give and take, give back, give satisfaction,
   indemnify, kick back, make amends, make compensation, make good,
   make reparation, make requital, make restitution, make retribution,
   make up for, make up to, offset, pay, pay back, pay damages,
   pay in kind, pay off, quit, reciprocate, recompense, recoup,
   rectify, redress, refund, reimburse, remunerate, requite, restore,
   retaliate, return, return the compliment, reward, set right,
   square, square with, yield a profit