Clod (3)
I believe the answer is:
oaf
'clod' is the definition.
(I know that clod is a class)
This is all the clue.
(Other definitions for oaf that I've seen before include "Stupid lout" , "A clumsy or stupid person" , "Clod" , "Boor or lout" , "Lout, lummox" .)