Philosopher to let sari out (9)
I believe the answer is:
aristotle
'philosopher' is the definition.
(I know that Aristotle is a philosopher)
'to let sari out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'to'+'let'+'sari'='toletsari'
'toletsari' anagrammed gives 'ARISTOTLE'.
(Other definitions for aristotle that I've seen before include "Peripatetic teacher" , "Totaliser (anag) - ancient Greek" , "Realist to be like great Greek philosopher" , "Thinking Greek" , "Ancient Greek philosopher" .)