Webster's Revised Unabridged Dictionary · 1913

(Physiology) Maintaining a uniform body temperature, usually above the ambient temperature; hamatothermal; homothermic; warm-blooded; -- applied to warm-bodied animals such as birds and mammals, because they maintain a nearly uniform temperature in spite of the great variations in the surrounding air; in distinct from the cold-blooded (poikilothermal) animals, whose body temperature follows the variations in temperature of the surrounding medium.