Wear down (6)
'wear down' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for abrade that I've seen before include "Day breaks? > Start as before" , "A beard (anag.)" , "Shave" , "Scratch" , "Rub off or scrape away" .)
'wear down' is the definition.
(to erode is to wear down or decay)
This is the entire clue.
(Other definitions for erode that I've seen before include "go to pieces!" , "Grind down" , "Gradually wear away" , "Gradually destroy" , "'Deteriorate, wear away (5)'" .)
(Other definitions for degrade that I've seen before include "Break down; debase" , "Cheapen, bring disgrace on" , "Deprive of dignity" , "Decompose chemically" , "Break down, deteriorate" .)