Unusually stoical, extremely smooth, medieval annotator (9)
I believe the answer is:
scholiast
'medieval annotator' is the definition.
(I've seen this before)
'unusually stoical extremely smooth' is the wordplay.
'unusually' indicates anagramming the letters.
'extremely' suggests removing the centre.
'smooth' with its centre removed is 'sh'.
'stoical'+'sh'='stoicalsh'
'stoicalsh' anagrammed gives 'SCHOLIAST'.
(Other definitions for scholiast that I've seen before include "commentator" , "Medieval annotator" .)