Top of a ridge (5)
I believe the answer is:
crest
'top of a ridge' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for crest that I've seen before include "Top of a ridge/wave" , "Top line of a hill, mountain, or wave" , "Summit - emblem - cockscomb" , "Surmount" , "Head" .)