Summit; crest (4)
I believe the answer is:
brow
This clue is a double definition.
'summit' is the first definition.
(I know that brow is a type of summit)
'crest' is the second definition.
(I know that brow is a type of crest)
(Other definitions for brow that I've seen before include "Peak of a hill" , "Mopped part of the head" , "Hill part -- head part" , "Crest" , "Forehead, sometimes knitted" .)