A parallelogram with four right angles (9)
I believe the answer is:
rectangle
'a parallelogram with four right angles' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for rectangle that I've seen before include "Figure on plane" , "regular sort of figure" , "Shape of football pitch" , "Parallelogram with four right angles" , "Four sides involved in this" .)