1. Describing an organism; such as, a mammal or bird, that maintains its body temperature at a stable level largely independent of (and typically higher than) the ambient temperature, primarily using generation of heat internal to the animal.
2. Heat absorbing; as, in a chemical reaction.

1. A chemical reaction during which heat is absorbed.
2. Warm-blooded animals; such as, birds or mammals; maintaining a body temperature largely independent of the temperature of the environment; homoiothermic.
3. Characterized by, or attended with, the absorption of heat.
4. Also known as homoiotherm.