The Collaborative International Dictionary of English v.0.48:

Resentment \Re*sent"ment\ (-ment), n. [F. ressentiment.]
   1. The act of resenting.
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   2. The state of holding something in the mind as a subject of
      contemplation, or of being inclined to reflect upon
      something; a state of consciousness; conviction; feeling;
      impression. [Obs.]
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            He retains vivid resentments of the more solid
            morality.                             --Dr. H. More.
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            It is a greater wonder that so many of them die,
            with so little resentment of their danger. --Jer.
                                                  Taylor.
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   3. In a good sense, satisfaction; gratitude. [Obs.]
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            The Council taking notice of the many good services
            performed by Mr. John Milton, . . . have thought fit
            to declare their resentment and good acceptance of
            the same.                             --The Council
                                                  Book (1651).
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   4. In a bad sense, strong displeasure; anger; hostility
      provoked by a wrong or injury experienced.
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            Resentment . . . is a deep, reflective displeasure
            against the conduct of the offender.  --Cogan.
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   Syn: Anger; irritation; vexation; displeasure; grudge;
        indignation; choler; gall; ire; wrath; rage; fury.

   Usage: Resentment, Anger. Anger is the broader term,
          denoting a keen sense of disapprobation (usually with
          a desire to punish) for whatever we feel to be wrong,
          whether directed toward ourselves or others.
          Resentment is anger exicted by a sense of personal
          injury. It is, etymologically, that reaction of the
          mind which we instinctively feel when we think
          ourselves wronged. Pride and selfishness are apt to
          aggravate this feeling until it changes into a
          criminal animosity; and this is now the more common
          signification of the term. Being founded in a sense of
          injury, this feeling is hard to be removed; and hence
          the expressions bitter or implacable resentment. See
          Anger.
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                Anger is like
                A full-hot horse, who being allowed his way,
                Self-mettle tires him.            --Shak.
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                Can heavently minds such high resentment show,
                Or exercise their spite in human woe? --Dryden.
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WordNet (r) 3.0 (2006):

resentment
    n 1: a feeling of deep and bitter anger and ill-will [syn:
         resentment, bitterness, gall, rancor, rancour]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "resentment":
   Faustianism, acrimony, agitation, anger, animosity, animus,
   annoyance, antagonism, antipathy, anxiety, bitterness,
   cold comfort, disappointment, discontent, discontentedness,
   discontentment, disgruntlement, displeasure, dissatisfaction,
   dissatisfiedness, divine discontent, dudgeon, enmity, envy, fury,
   grudge, hate, hostility, huff, ill humor, ill will, indignation,
   ire, irritation, jealousy, malice, malignancy, malignity, miff,
   peevishness, petulance, pique, provocation, querulousness, rancor,
   rebelliousness, restiveness, restlessness, snuff, sourness, spite,
   sulkiness, umbrage, uneasiness, unfulfillment, unhappiness,
   unpleasure, unsatisfaction, upset, vexation of spirit