noun

1. act or process of respiring; breathing; inhaling and exhaling air
2. the processes by which a living organism or cell takes in oxygen from the air or water, distributes and utilizes it in oxidation, and gives off products of oxidation, esp. carbon dioxide
3. an analogous process in anaerobic organisms involving some substance other than free oxygen

Etymology: ME respiracioun < L respiratio < respiratus, pp.