Wrong answer to omit (5)
I believe the answer is:
amiss
'wrong' is the definition.
(I know that wrong can be written as amiss)
'answer to omit' is the wordplay.
'answer' becomes 'a' (abbreviation eg in Q and A).
'to omit' becomes 'miss' (synonyms).
'a'+'miss'='AMISS'
(Other definitions for amiss that I've seen before include "Wrongly" , "Wrong - awry" , "error" , "Unsuitable" , "Not quite right" .)