mitigator

from The Collaborative International Dictionary of English v.0.48

Mitigator \Mit"i*ga`tor\, n.
   One who, or that which, mitigates.
   [1913 Webster]

from Moby Thesaurus II by Grady Ward, 1.0

26 Moby Thesaurus words for "mitigator":
      alleviative, alleviator, anodyne, assuager, balm, calmative,
      cushion, dolorifuge, lenitive, moderator, modulator, mollifier,
      pacificator, pacifier, palliative, peacemaker, restraining hand,
      salve, sedative, shock absorber, soother, soothing syrup,
      stabilizer, temperer, tranquilizer, wiser head