Yield to gravity (3)
I believe the answer is:
sag
'yield to gravity' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sag that I've seen before include "Droop, sink in the middle" , "Sink (under load)" , "fall" , "Give way under pressure" , "Spinach as used in Indian cookery" .)