the compound adjective "warm-blooded" is a transparent formation from two native english elements. the old english root wearm (warm) is of germanic origin, ultimately from the pie root gʷʰer- meaning "warm, hot". the old english blōd (blood) also has germanic roots, likely from pie bhel- meaning "to thrive, bloom". the term was constructed in english to literally describe creatures "having warm blood," a physiological trait distinguishing mammals and birds from reptiles and fish. this literal meaning later extended metaphorically to describe humans with passionate or lively dispositions, completing the journey from a concrete physical description to an abstract character trait.

Structure: warm (sense) + blood (sense) + ed (sense) warm: from old english wearm, meaning having or giving a moderate degree of heat. blood: from old english blōd, meaning the red liquid circulating in the arteries and veins. ed: a suffix forming adjectives from nouns, meaning having or provided with.