Utter failing to eat nothing (5)
I believe the answer is:
voice
'utter' is the definition.
(voicing is a kind of uttering)
'failing to eat nothing' is the wordplay.
'failing' becomes 'vice' (vice can mean a moral failing).
'to eat' is an insertion indicator.
'nothing' becomes 'O' (O resembles 0).
'vice' going around 'o' is 'VOICE'.
(Other definitions for voice that I've seen before include "Wallop" , "Put into words" , "eg Bass" , "tenor, say" , "Sound with which one speaks" .)