Model question (5)
I believe the answer is:
poser
I believe this clue is a double definition.
'model' is the first definition.
(synonyms)
'question' is the second definition.
(poser is a kind of question)
(Other definitions for poser that I've seen before include "difficult puzzle" , "Sticky problem" , "Someone behaving so as to be noticed" , "one who has airs and graces" , "Problem set by the model" .)