Creature of the masses (3)
I believe the answer is:
ass
'creature' is the definition.
(donkey)
'of the masses' is the wordplay.
'of' indicates a hidden word.
'ASS' is hidden within 'the masses'.
(Other definitions for ass that I've seen before include "Horse hybrid" , "twit!" , "Donkey - one that's foolish" , "An American backside" , "Titania loved one" .)