Imperial advisor not quite ill-advised to enter (8)
I believe the answer is:
rasputin
'imperial advisor' is the definition.
(Russian mystic who advised Tsar Nicholas II)
'not quite ill-advised to enter' is the wordplay.
'not quite' means to remove the last letter.
'ill-advised' becomes 'rash' (both can mean unwise).
'to enter' becomes 'putin' (enter can mean to write down or put in).
'rash' with its last letter taken off is 'ras'.
'ras'+'putin'='RASPUTIN'
(Other definitions for rasputin that I've seen before include "Notorious Russian monk among puritans" , "sinister Russian" , "Notorious Russian monk at court of Tsar" , "Influential Russian mystic" , "Sinister adviser" .)