Rewrite prose essay essentially for teacher (9)
I believe the answer is:
professor
'teacher' is the definition.
(thesaurus)
'rewrite prose essay essentially for' is the wordplay.
'rewrite' is an anagram indicator.
'essentially' means to look at the middle letters.
The middle of 'essay' is 's'.
'prose'+'s'+'for'='prosesfor'
'prosesfor' anagrammed gives 'PROFESSOR'.
(Other definitions for professor that I've seen before include "One who claims" , "Member of an academic faculty" , "Head of faculty, department" , "University lecturer" , "chairman?" .)