Reaches a peak (6)
I believe the answer is:
crests
'reaches a peak' is the definition.
(cresting is a kind of reaching a peak)
This is all the clue.
(Other definitions for crests that I've seen before include "Emblems of families" , "summits" , "Topmost ridges of mountains" , "Tufts on birds' heads, or tops of waves" .)