Sit (4)
I believe the answer is:
pose
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sit</span>' is the definition.<br/ ><span class="explanation-format__explanation">(as in sitting for a painter)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for pose that I've seen before include "Sit as model" , "Sit for a painter" , "position" , "Pretend to be somebody else" , "Present (problem), sit" .)