Rocks glimpsed among the waves! (5)
I believe the answer is:
tiara
If this is the answer I cannot explain how the clue works.
Can you help me to learn more?
(Other definitions for tiara that I've seen before include "Ornamental crescent-shaped headdress or Pope's diadem" , "Woman's headdress for very formal occasions" , "it goes to one's head!" , "Jewelled headwear" , "Jewelled headband" .)