Make a mistake with one zero? We object it’s wrong (9)
I believe the answer is:
erroneous
'it's wrong' is the definition.
(similar in meaning)
'make a mistake with one zero? we object' is the wordplay.
'make a mistake' becomes 'err' (to err is to make an error).
'with' says to put letters next to each other.
'we object' becomes 'us' (object pronoun for 'we').
'err'+'one'+'o'+'us'='ERRONEOUS'
(Other definitions for erroneous that I've seen before include "not right" , "Incorrect, wrong" , "Mistaken, in error" , "Mistaken - inaccurate" , "with mistakes" .)