Creature in glasses (3)
I believe the answer is:
ass
'creature' is the definition.
(donkey)
'in glasses' is the wordplay.
'in' indicates a hidden word.
'ASS' is hidden in the letters of 'glasses'.
(Other definitions for ass that I've seen before include "Clot" , "Silly fool or beast of burden" , "Trump's behind" , "mug" , "A donkey or an idiot" .)