Weary sound (4)
I believe the answer is:
sigh
'weary sound' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for sigh that I've seen before include "Vocal expression of weariness" , "Exhale wearily" , "Moan softly" , "Sound of regret" , "Utterance made by exhaling audibly" .)