Wear down little rodent in the middle (5)
I believe the answer is:
erode
'wear down' is the definition.
(I've seen this before)
'little rodent in the middle' is the wordplay.
'in the middle' indicates a hidden word (the answer is in the middle of the clue).
'ERODE' is hidden in the letters of 'little rodent'.
(Other definitions for erode that I've seen before include "Grind down" , "Wear away with weather" , "Slowly remove" , "Corrode" , "Abrade" .)