Nobleman ahead of schedule for the most part (4)
I believe the answer is:
earl
'nobleman' is the definition.
(earl is a kind of nobleman)
'ahead of schedule for the most part' is the wordplay.
'ahead of schedule' becomes 'early' (I've seen this before).
'for the most part' means to remove the last letter.
'early' with its last letter taken off is 'EARL'.
(Other definitions for earl that I've seen before include "Countess his wife" , "UK nobleman ranking between marquess and viscount" , "Titled man" , "Count" , "Sandwich perhaps" .)