Constitute a pretence (4)
I believe the answer is:
pose
I believe this clue is a double definition.
'constitute' is the first definition.
(posing is a kind of constituting)
'a pretence' is the second definition.
(pose is a kind of pretence)
(Other definitions for pose that I've seen before include "Models do it for photographic or artistic purposes" , "Attitudinise" , "Sit (for an artist)" , "Sit for a painter" , "Stance - attitude" .)