Idiot in Honiton (3)
I believe the answer is:
nit
'idiot' is the definition.
(nit can mean a stupid person)
'in honiton' is the wordplay.
'in' says the answer is hidden in the clue.
'NIT' is hidden within 'honiton'.
(Other definitions for nit that I've seen before include "Muggins" , "Louse-egg" , "Cause of much head-scratching" , "Egg of parasitic insect" , "Eg of louse" .)