Many-sided figure (7)
I believe the answer is:
polygon
'many-sided figure' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for polygon that I've seen before include "Closed plane figure with three or more straight sides" , "Geometric figure with five or more sides" , "Many-sided plane figure" , "Figure with many sides" , "Closed plane figure bounded by straight sides" .)