Bread with top cut off by fool (3)
I believe the answer is:
oaf
'fool' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for oaf that I've seen before include "Idiot" , "Boorish person" , "Barbarian" , "buffoon" , "Awkward, clumsy person" .)