Source : Webster's Revised Unabridged Dictionary (1913)

Supererogation \Su`per*er`o*ga"tion\, n. [L. supererogatio a
   payment in addition.]
   The act of supererogating; performance of more than duty or
   necessity requires.

   {Works of supererogation} (R. C. Ch.), those good deeds
      believed to have been performed by saints, or capable of
      being performed by men, over and above what is required
      for their own salvation.

Source : WordNet®

supererogation
     n : an effort above and beyond the call of duty