Quadrilateral – wrist bone (9)
I believe the answer is:
trapezoid
This clue is a double definition.
'quadrilateral' is the first definition.
(I know that trapezoid is a type of quadrilateral)
'wrist bone' is the second definition.
(I know that trapezoid is a type of wrist bone)
(Other definitions for trapezoid that I've seen before include "Form of quadrilateral" , "Figure" , "Prize toad (anag.)" , "Type of quadrilateral" .)