A cold-blooded animal has a body temperature that varies along with the outdoor temperature, and a cold-blooded person is someone who seems to feel no emotions. Your pet lizard may love you, but she's still cold-blooded.

During a hot, sunny day, a cold-blooded animal like a snake experiences a rise in body temperature, which it can only moderate by finding a shady spot to hide. When the sun goes down at night, a snake's body temperature falls. Cold-blooded people, on the other hand, regulate their body temperature even when it's chilly outside, like other warm-blooded animals. They're cruel and unfeeling, though. This meaning comes from the old-fashioned belief that blood temperature rises with emotion.

Definitions of cold-blooded
  1. adjective
    having cold blood (in animals whose body temperature is not internally regulated)
    ectothermic, heterothermic, poikilothermic, poikilothermous
    of animals except birds and mammals; having body temperature that varies with the environment
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    having warm blood (in animals whose body temperature is internally regulated)
    homeothermic, homoiothermic, homothermic
    of birds and mammals; having constant and relatively high body temperature
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  2. adjective
    without compunction or human feeling
    synonyms: cold, inhuman, insensate
    reflecting lack of pity or compassion
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