As a verb: to be very angry or to inhale and exhale smoke; as a noun: a strong-smelling gas or vapor released from something burning or chemical.
From Latin 'fumus' meaning smoke or vapor, which came from an Indo-European root related to 'smoke.' The sense of being angry developed because angry people were imagined as 'smoking' with rage.
Medieval and Renaissance writers loved describing furious people as 'fuming'—they literally thought anger created hot vapors that rose from the body like smoke, a theory that came from ancient medicine's belief in bodily humors, so the metaphor is actually rooted in how people physically imagined anger working.
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