Worn down (6)
I believe the answer is:
eroded
'worn down' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for eroded that I've seen before include "Worn away, ground down" , "Worn away by time, wind or water" , "Wore away" , "Eaten away" , "Worn away by weather or water" .)