Head dismissing learner as fool (3)
I believe the answer is:
oaf
'fool' is the definition.
(I've seen this before)
'head dismissing learner' is the wordplay.
'head' becomes 'loaf' (slang term for the head).
'dismissing' indicates named letters should be taken away.
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'loaf' with 'l' taken out is 'OAF'.
'as' is the link.
(Other definitions for oaf that I've seen before include "A clumsy or stupid person" , "Clumsy fool" , "An ill-mannered lout" , "Barbarian" , "Bumpkin" .)