Audible exhalation (4)
I believe the answer is:
sigh
'audible exhalation' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sigh that I've seen before include "Moan softly" , "Exhale wearily" , "Exhale deeply" , "Sound of despondency" , "Audible breath expressing weariness" .)