The Collaborative International Dictionary of English v.0.48:

Regret \Re*gret"\, v. t. [imp. & p. p. Regretted (-t[e^]d); p.
   pr. & vb. n. Regretting.] [F. regretter, OF. regreter; L.
   pref. re- re- + a word of Teutonic origin; cf. Goth.
   gr[=e]tan to weep, Icel. gr[=a]ta. See Greet to lament.]
   To experience regret on account of; to lose or miss with a
   sense of regret; to feel sorrow or dissatisfaction on account
   of (the happening or the loss of something); as, to regret an
   error; to regret lost opportunities or friends.
   [1913 Webster]

         Calmly he looked on either life, and here
         Saw nothing to regret, or there to fear. --Pope.
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         In a few hours they [the Israelites] began to regret
         their slavery, and to murmur against their leader.
                                                  --Macaulay.
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         Recruits who regretted the plow from which they had
         been violently taken.                    --Macaulay.
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The Collaborative International Dictionary of English v.0.48:

Regret \Re*gret"\ (r?*gr?t"), n. [F., fr. regretter. See
   Regret, v.]
   1. Pain of mind on account of something done or experienced
      in the past, with a wish that it had been different; a
      looking back with dissatisfaction or with longing; grief;
      sorrow; especially, a mourning on account of the loss of
      some joy, advantage, or satisfaction. "A passionate regret
      at sin." --Dr. H. More.
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            What man does not remember with regret the first
            time he read Robinson Crusoe?         --Macaulay.
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            Never any prince expressed a more lively regret for
            the loss of a servant. --Clarendon.
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            From its peaceful bosom [the grave] spring none but
            fond regrets and tender recollections. --W. Irving.
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   2. Dislike; aversion. [Obs.] --Dr. H. More.
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   Syn: Grief; concern; sorrow; lamentation; repentance;
        penitence; self-condemnation.

   Usage: Regret, Remorse, Compunction, Contrition,
          Repentance. Regret does not carry with it the energy
          of remorse, the sting of compunction, the sacredness
          of contrition, or the practical character of
          repentance. We even apply the term regret to
          circumstance over which we have had no control, as the
          absence of friends or their loss. When connected with
          ourselves, it relates rather to unwise acts than to
          wrong or sinful ones. --C. J. Smith.
          [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

67 Moby Thesaurus words for "regret":
   abject apology, acknowledgment, affliction, anguish, apologies,
   apology, attrition, ayenbite of inwit, be sorry for, bemoan,
   bewail, bitterness, breast-beating, care, compunction, confession,
   contriteness, contrition, demur, deplore, deprecate,
   disappointment, disapprove, dole, dolor, excuse, feel sorry for,
   grief, grieve, guilt, heartache, heartbreak, lament, mea culpa,
   mourn, mournfulness, pangs of conscience, penitence, qualm,
   refusal, regretfulness, regrets, regretting, remorse,
   remorse of conscience, remorsefulness, repent, repentance, repine,
   repining, rue, rue the day, ruefulness, sadness, scruple,
   second thoughts, self-condemnation, self-reproach, shame,
   shamefacedness, shamefastness, shamefulness, sorriness, sorrow,
   weep over, wistfulness, woe