Sags (6)
I believe the answer is:
droops
'sags' is the definition.
('droop' can be a synonym of 'sag')
This is all the clue.
(Other definitions for droops that I've seen before include "Hangs loosely or laxly" , "Grows weak and hangs down" , "'Sags, wilts (6)'" , "Languishes" , "Sags through tiredness" .)