cold-blooded (adj.)

• 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