Fool in glasses (3)
I believe the answer is:
ass
'fool' is the definition.
(both can mean a stupid person)
'in glasses' is the wordplay.
'in' indicates a hidden word.
'ASS' can be found hidden inside 'glasses'.
(Other definitions for ass that I've seen before include "slow-witted person" , "Silly fellow in passionate state" , "twit!" , "Democratic mascot" , "Transport for a wise man - or a fool" .)