With all due thinking...
I think a Diamond shape will befit your answer. So; The real answer is "Rhomboid"
The reason is that...
A rhomboid has four parallel sides. The opposite sides are equal, but the corners do not form right angles. Think of a rectangle that is slanted(a.k.a diamond) Thats what a Rhomboid is...
A parallelogram that dosent have equal sides is not a rhombus; and which dosent have Right angles are not rectangles and hence cannot be aquares either.
So in all Way a Rhomboid will mark the answer for your question.
Hope it helps..
Regards,
Leukonov/Olegion.