Nothing fixes a fixer (4)
I believe the answer is:
nail
'fixer' is the definition.
Both the definition and answer are singular nouns.
Perhaps you can see an association between them that I don't see?
'nothing fixes a' is the wordplay.
I cannot quite understand how this works, but
'a' is found in the answer.
'nothing' could be 'nil' (eg nil is zero in football) and 'nil' is found in the remaining letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for nail that I've seen before include "one wouldn't want in one's coffin?" , "Handy tip" , "Fixing pin" , "It needs a hammer (or a file?)" , "Fixer (on finger?)" .)