Not sure about a nice turn (9)
I believe the answer is:
uncertain
'not sure' is the definition.
('uncertain' is the opposite to 'sure')
'about a nice turn' is the wordplay.
'about' is an anagram indicator.
'a'+'nice'+'turn'='aniceturn'
'aniceturn' is an anagram of 'UNCERTAIN'.
(Other definitions for uncertain that I've seen before include "in the lap of the gods" , "Not definitely known" , "dubious" , "Doubtful, indecisive" , "Unsure" .)