(n.) One who, or that which, assuages.

alleviating alleviator analgesic anesthetic anodyne assuager assuasive balm balmy balsamic benumbing calmant calmative cathartic cleansing cushion deadening demulcent disburdening disencumbering dolorifuge dulling easing emollient lenitive lightening mitigating mitigative mitigator moderator modulator mollifier numbing pacificator pacifier pain-killing palliative peacemaker purgative relieving remedial restraining hand salve sedative shock absorber softening soother soothing soothing syrup stabilizer subduing temperer tranquilizer unburdening wiser head