Source : Webster's Revised Unabridged Dictionary (1913)

Mitigative \Mit"i*ga*tive\, a. [L. mitigativus: cf. F.
   mitigatif.]
   Tending to mitigate; alleviating.

Source : WordNet®

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