Lad to bury duke's corpse (4)
I believe the answer is:
body
'corpse' is the definition.
(I've seen this before)
'lad to bury duke's' is the wordplay.
'lad' becomes 'boy' (I've seen this in another clue).
'to bury' means one lot of letters goes inside another (inserted letters are buried inside).
'duke' becomes 'd' (abbreviation).
'boy' going around 'd' is 'BODY'.
(Other definitions for body that I've seen before include "Group of persons thought of as an entity" , "Non-verbal communication?" , "Individual" , "Physique" , "Person - corporation" .)