respiration

Short definition from Wiktionary

Noun

1. 1
   The process of inhaling and exhaling; breathing, breath.
2. 2
   An act of breathing; a breath.
3. 3
   Any similar process in an organism that lacks lungs that exchanges gases with its environment.
4. 4
   The process by which cells obtain chemical energy by the consumption of oxygen and the release of carbon dioxide.