Duffer (5)
I believe the answer is:
dunce
'duffer' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for dunce that I've seen before include "School fool" , "Unkind word for slow learner" , "Halfwit" , "Dull chap" , "Term of ridicule applied to followers of John Duns Scotus" .)