Why is the ninth month called September?
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" (cf. Old High German bradam, German Brodem "breath, steam"), from PIE root *gwhre- "to breathe, smell."
The air inhaled and exhaled in respiration.
A single respiration.