Margins of wedge-shaped objects (5)
I believe the answer is:
edges
'margins' is the definition.
('edge' can be a synonym of 'margin')
'of wedge-shaped objects' is the wordplay.
'of' indicates the answer is hidden within the clue.
'EDGES' is hidden in the letters of 'wedge shaped objects'.
(Other definitions for edges that I've seen before include "Boundaries of a surface" , "Fringes" , "Sharpened sides of knives etc" , "Sharpened sides of blades" , "Des, e.g. (anag.)" .)