A model problem? (5)

I believe the answer is:

poser

I believe this is a double definition.

'a model' is the first definition.
(I know that Model can be written as poser)

'problem?' is the second definition.
(I know that poser is a type of problem)

(Other definitions for poser that I've seen before include "Maybe model" , "Tricky question" , "Puzzle using ropes" , "Particularly baffling problem" , "Hard question" .)

I've seen this clue in the Evening Standard.

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