Centaur in trouble? Not sure (9)
I believe the answer is:
uncertain
'not sure' is the definition.
(I know this)
'centaur in trouble?' is the wordplay.
'trouble?' indicates an anagram (I've seen 'troubled' mean this).
'centaur'+'in'='centaurin'
'centaurin' with letters rearranged gives 'UNCERTAIN'.
(Other definitions for uncertain that I've seen before include "In doubt" , "up in the air" , "in the lap of the gods" , "Unsure" , "Doubtful, indecisive" .)