Geometrical shape (6)
I believe the answer is:
oblong
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">geometrical shape</span>' is the definition.<br/ ><span class="explanation-format__explanation">(old-fashioned term for a rectangle)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for oblong that I've seen before include "Plane figure that deviates from a square by elongation" , "tablet format?" , "Cab" , "Oval" , "Elongated rectangle" .)