Source : Webster's Revised Unabridged Dictionary (1913)

Mitigatory \Mit"i*ga*to*ry\, a.
   Tending to mitigate or alleviate; mitigative.

Source : WordNet®

mitigatory
     adj : moderating pain or sorrow by making it easier to bear [syn:
           {alleviative}, {alleviatory}, {lenitive}, {mitigative},
            {palliative}]