Bite lip (4)
I believe the answer is:
edge
This clue is a double definition.
'bite' is the first definition.
(I've seen this before)
'lip' is the second definition.
(I've seen this before)
(Other definitions for edge that I've seen before include "Sharp ridge" , "Rim - move gradually" , "Sharpened side of blade" , "Inch; border" , "The part farthest from the middle" .)