Lump — oaf (4)
I believe the answer is:
clod
I believe this clue is a double definition.
'lump' is the first definition.
(I know that lump can be written as clod)
'oaf' is the second definition.
(I know that oaf can be written as clod)
(Other definitions for clod that I've seen before include "Compact mass - stupid person" , "Piece of earth" , "Lump of earth/clay" , "dope?" , "Idiot" .)