Exhalation (6)
I believe the answer is:
breath
'exhalation' is the definition.
(synonyms)
This is all the clue.
(Other definitions for breath that I've seen before include "Air in an out of the lungs" , "Bather (anag.)" , "Slight movement of air" , "An inhalation and exhalation" , "Inhale and exhale air" .)