breathyoudaoicibaDictYouDict[breath 词源字典]
breath: [OE] Breath comes ultimately from the Indo-European base *bhrē- ‘burn, heat’ (source also of braise, breed, brood, and probably brawn), and in its original Indo-European form *bhrētos appears to have meant something like the ‘steam, vapour, etc given off by something burning or cooking’. When it reached Old English, via Germanic *brǣthaz, it still meant ‘smell’ or ‘exhalation’, and it was not in fact until as late as the 14th century that this notion of ‘exhalation’ came to be applied to human or animal respiration (the main Old English word for ‘breath’ had been ǣthm, which German still has in the form atem).

The verb breathe is 13thcentury.
=> braise, brawn, breed, brood[breath etymology, breath origin, 英语词源]
breath (n.)youdaoicibaDictYouDict
Old English bræð "odor, scent, stink, exhalation, vapor" (Old English word for "air exhaled from the lungs" was æðm), from Proto-Germanic *bræthaz "smell, exhalation" (cognates: Old High German bradam, German Brodem "breath, steam"), from PIE root *gwhre- "to breathe, smell."