Correct or sure one is wrong (9)
I believe the answer is:
erroneous
'is wrong' is the definition.
(similar in meaning)
'correct or sure one' is the wordplay.
'correct' indicates an anagram.
'or'+'sure'+'one'='orsureone'
'orsureone' anagrammed gives 'ERRONEOUS'.
(Other definitions for erroneous that I've seen before include "with mistakes" , "Mistaken, in error" , "not right" , "Incorrect, wrong" , "Mistaken - inaccurate" .)