Advance furtively (4)
(Other definitions for edge that I've seen before include "Hem" , "Lip; advantage" , "Boundary; advantage" , "Border - advantage" , "Bite" .)
'advance furtively' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sidle that I've seen before include "sidewalk" , "Move like a crab" , "Walk sideways in furtive manner" , "Inch along" , "Slide (anag.)" .)