The Collaborative International Dictionary of English v.0.48:

Forgiveness \For*give"ness\, n. [AS. forgifnes.]
   1. The act of forgiving; the state of being forgiven; as, the
      forgiveness of sin or of injuries.
      [1913 Webster]

            To the Lord our God belong mercies and
            forgivenesses.                        --Dan. ix. 9.
      [1913 Webster]

            In whom we have . . . the forgiveness of sin. --Eph.
                                                  i. 7.
      [1913 Webster]

   2. Disposition to pardon; willingness to forgive.
      [1913 Webster]

            If thou, Lord, shouldest mark iniquities, O Lord,
            who shall stand? But there is forgiveness with thee,
            that thou mayest be feared.           --Ps. cxxx. 3,
                                                  4.

   Syn: Pardon, remission.

   Usage: Forgiveness, Pardon. Forgiveness is Anglo-Saxon,
          and pardon Norman French, both implying a giving back.
          The word pardon, being early used in our Bible, has,
          in religious matters, the same sense as forgiveness;
          but in the language of common life there is a
          difference between them, such as we often find between
          corresponding Anglo-Saxon and Norman words. Forgive
          points to inward feeling, and suppose alienated
          affection; when we ask forgiveness, we primarily seek
          the removal of anger. Pardon looks more to outward
          things or consequences, and is often applied to
          trifling matters, as when we beg pardon for
          interrupting a man, or for jostling him in a crowd.
          The civil magistrate also grants a pardon, and not
          forgiveness. The two words are, therefore, very
          clearly distinguished from each other in most cases
          which relate to the common concerns of life.
          [1913 Webster]

WordNet (r) 3.0 (2006):

forgiveness
    n 1: compassionate feelings that support a willingness to
         forgive
    2: the act of excusing a mistake or offense [syn: forgiveness,
       pardon]

Moby Thesaurus II by Grady Ward, 1.0:

66 Moby Thesaurus words for "forgiveness":
   Lethe, absentmindedness, absolution, acquittal, acquittance,
   allowance, amnesty, benevolence, clearance, clearing, clemency,
   commiseration, compassion, compurgation, condolence,
   decay of memory, destigmatization, destigmatizing, discharge,
   disculpation, dismissal, exculpation, excuse, exoneration, favor,
   feeling, forbearance, forgetfulness, forgetting, grace,
   hazy recollection, heedlessness, humanity, indulgence, kindness,
   leniency, mercifulness, mercy, mitigation, nepenthe, nirvana,
   obliteration, oblivion, obliviousness, pardon, pathos, pity,
   purgation, purging, quarter, quietus, quittance, release, relief,
   remission, reprieve, ruth, self-pity, short memory, shrift,
   sympathy, tolerance, unmindfulness, verdict of acquittal,
   vindication, waters of oblivion