The Collaborative International Dictionary of English v.0.48:

Indignation \In`dig*na"tion\, n. [F. indignation, L. indignatio.
   See Indign.]
   [1913 Webster]
   1. The feeling excited by that which is unworthy, base, or
      disgraceful; anger mingled with contempt, disgust, or
      abhorrence. --Shak.
      [1913 Webster]

            Indignation expresses a strong and elevated
            disapprobation of mind, which is also inspired by
            something flagitious in the conduct of another.
                                                  --Cogan.
      [1913 Webster]

            When Haman saw Mordecai in the king's gate, that he
            stood not up, nor moved for him, he was full of
            indignation against Mordecai.         --Esther v. 9.
      [1913 Webster]

   2. The effect of anger; punishment. --Shak.
      [1913 Webster]

            Hide thyself . . . until the indignation be
            overpast.                             --Is. xxvi.
                                                  20.

   Syn: Anger; ire wrath; fury; rage. See Anger.
        [1913 Webster]

WordNet (r) 3.0 (2006):

indignation
    n 1: a feeling of righteous anger [syn: indignation,
         outrage]

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "indignation":
   anger, annoyance, ban, blackball, blackballing, choler, complaint,
   dim view, disagreement, disappointment, disapprobation,
   disapproval, discontent, discontentedness, discontentment,
   disenchantment, disesteem, disfavor, disgruntlement, disillusion,
   disillusionment, displeasure, disrespect, dissatisfaction, dissent,
   distaste, exasperation, exclusion, fury, indignant displeasure,
   ire, irritation, low estimation, low opinion, mad, objection,
   opposition, opposure, ostracism, protest, rage, rejection,
   resentment, righteous indignation, thumbs-down, unhappiness,
   vexation, wrath