Worn down advantage (6)
I believe the answer is:
ground
This could be a double definition.
'worn down' is the first definition.
(ground down)
'advantage' is the second definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
Can you help me to learn more?
(Other definitions for ground that I've seen before include "Earth; stop from flying" , "Pulverised; earth" , "Stop (a pilot) flying" , "Solid part of the earth's surface" , "Land; reduced to powder" .)