Nerve broken? Not at all (5)
I believe the answer is:
never
'not at all' is the definition.
(I've seen this in another clue)
'nerve broken?' is the wordplay.
'broken?' indicates anagramming the letters.
'nerve' anagrammed gives 'NEVER'.
(Other definitions for never that I've seen before include "At no time whatever" , "Surely not" , "No way" , "when pigs fly" , "Certainly not!" .)