Perfectionist exercises Italian poet endlessly (6)
I believe the answer is:
pedant
'perfectionist' is the definition.
(thesaurus)
'exercises italian poet endlessly' is the wordplay.
'exercises' becomes 'pe' (Physical Education class).
'italian poet' becomes 'Dante' (Dante Alighieri).
'endlessly' means to remove the last letter.
'dante' with its last letter taken off is 'dant'.
'pe'+'dant'='PEDANT'
(Other definitions for pedant that I've seen before include "One excessively concerned with minor detail" , "Panted like stickler for accuracy" , "Panted (anag.)" , "One concerned with excessive detail" , "One who insists on minor details, may be a conceited know-all" .)