Some of the rodents gnaw away (5)
I believe the answer is:
erode
'gnaw away' is the definition.
(thesaurus)
'some of the rodents' is the wordplay.
'some of' says the answer is hidden in the clue.
'ERODE' is hidden in the letters of 'the rodents'.
(Other definitions for erode that I've seen before include "Gradually wear away" , "Gradually destroy" , "Abrade" , "go to pieces!" , "'Deteriorate, wear away (5)'" .)