Parallelogram (8)
I believe the answer is:
rhomboid
'parallelogram' is the definition.
(I know that rhomboid is a type of parallelogram)
This is all the clue.
(Other definitions for rhomboid that I've seen before include "Describing a type of parallelogram" , "Shape" , "Quadrilateral in which only opposite sides and angles are equal" , "Parallelogram, but not square" , "Form of parallelogram" .)