From Old English 'brǣþ,' which originally meant 'smell' or 'odor' — named for what you could detect on an exhalation, not respiration itself.
The air taken into or expelled from the lungs; the process of breathing.
From Old English 'braeth' (odor, smell, exhalation, vapor), from Proto-Germanic *brethan (smell, exhalation, vapor), possibly connected to PIE *gwher- (warm, hot) or *bhreh1- (to heat, to burn). Crucially, the original meaning was 'smell' or 'vapor,' not the act of inhaling: breath was first named for what you could smell on it, not for the respiratory act itself. The semantic shift from odor to respiration happened gradually in Middle English. Old English had a separate word 'aethm' (also breath, vapor) which is
Old English 'brǣþ' originally meant 'smell' or 'stench,' not 'breath' in the modern sense. 'Breath' was named for what you could smell on it — the odor of the exhalation. The shift from 'smell' to 'respiration' happened gradually during the Middle English period, as the word lost its olfactory connotation and became purely respiratory