Circles and squares (6)
I believe the answer is:
shapes
'circles and squares' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for shapes that I've seen before include "Forms, outlines" , "Specific forms of things" , "Oblong and square, say" , "10, 17 and 22, for example" , "Oblong, square etc" .)