Respiration (6)
I believe the answer is:
breath
'respiration' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for breath that I've seen before include "Air drawn in and expelled out" , "Bertha (anag.)" , "Air that's inhaled and exhaled" , "Bather (anag.)" , "Inhale and exhale air" .)