Upper part of a wave (5)
I believe the answer is:
crest
(Other definitions for crest that I've seen before include "Highest point" , "Top of a ridge/wave" , "Plume on a helmet" , "top position" , "Head" .)
I believe the answer is:
crest
(Other definitions for crest that I've seen before include "Highest point" , "Top of a ridge/wave" , "Plume on a helmet" , "top position" , "Head" .)