Surprisingly leave rich knight (9)
I believe the answer is:
chevalier
'knight' is the definition.
(thesaurus)
'surprisingly leave rich' is the wordplay.
'surprisingly' indicates anagramming the letters.
'leave'+'rich'='leaverich'
'leaverich' with letters rearranged gives 'CHEVALIER'.
(Other definitions for chevalier that I've seen before include "noble rider?" , "novelist" , "courteous type" , "order of merit" , "Each viler than the strange knight" .)