Sharp surface (4)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
edge
'sharp surface' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for edge that I've seen before include "Inch; border" , "Rim or sharp side of knife" , "Sidle, lip" , "Margin, extremity" , "Brink or border" .)