Having an unregulated body temperature; ectothermic. / Lacking emotion or compunction.

(idiomatic) In a ruthless and unfeeling manner, particularly as applied to first-degree murder committed without provocation and with malice aforethought.

(obsolete outside the phrase in cold blood) A state of mild or low emotions, previously understood as a condition whereby the blood has not been appreciably heated by emotional intensity.

In a cold-blooded manner.

the state of being cold-blooded