Sit for a picture (4)
I believe the answer is:
pose
'sit for a picture' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for pose that I've seen before include "Pretend to be somebody else" , "Present (problem), sit" , "Affectation" , "Sit; attitude" , "Sit for picture" .)