Cold-blooded means taking body heat from the surroundings. Cold-blooded reptiles, a cold-blooded animal, cold-blooded murder.
The blood is not actually cold, since a lizard in the sun is warmer than you are, and the animal simply cannot make its own heat. The figurative sense means without feeling, and cold-blooded murder is the standard phrase.
1adjectivecold-bloodedTaking body heat from the surroundings.
“Snakes are cold-blooded, so they lie in the sun to warm up.”
cold-blooded is a quality.
From cold blood plus -ed, from the old belief that the blood carried an animal's heat.
From cold blood + ed.
Etymology from Wiktionary, CC BY-SA
Practised in Dinosaurs & Prehistory