Puzzle for a model? (5)
I believe the answer is:
poser
This clue is a double definition.
'puzzle' is the first definition.
(poser can mean a mystery or puzzle)
'for a model?' is the second definition.
(synonyms)
(Other definitions for poser that I've seen before include "This person's affected" , "What's difficult" , "difficult puzzle" , "Question; one trying to impress" , "Particularly baffling problem" .)