Source : Webster's Revised Unabridged Dictionary (1913)

Exculpation \Ex`cul*pa"tion\, n. [Cf. LL. exculpatio.]
   The act of exculpating from alleged fault or crime; that
   which exculpates; excuse.

         These robbers, however, were men who might have made
         out a strong case in exculpation of themselves.
                                                  --Southey.

Source : WordNet®

exculpation
     n 1: a defense of some offensive behavior or some failure to keep
          a promise etc.; "he kept finding excuses to stay";
          "every day he had a new alibi for not getting a job";
          "his transparent self-justification was unacceptable"
          [syn: {excuse}, {alibi}, {self-justification}]
     2: the act of freeing from guilt or blame