Worn-out flap (4)
I believe the answer is:
beat
I believe this clue is a double definition.
'worn-out' is the first definition.
(thesaurus)
'flap' is the second definition.
('beat' can be a synonym of 'flap')
(Other definitions for beat that I've seen before include "Musical rhythm" , "Defeat; pulsate" , "Defeat; throb" , "Worst round" , "Flog" .)