Synonyms and related words :
apathetic, barbaric, barbarous, brutal, callous, cool, cruel, dispassionate, heartless, imperturbable, indifferent, inhuman, insensitive, merciless, pitiless, poikilothermic, ruthless, savage, steely, stony, thick-skinned, uncaring, unemotional, unexcited, unfeeling, unimpassioned, unmoved, unresponsive, unsympathetic, vicious,