Sounds like one bound on the crest of a wave (4)

I believe the answer is:

surf

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'wave' is the definition.
(I know that surf is a type of wave)

I don't understand how the rest of the clue works.

(Other definitions for surf that I've seen before include "Sea foam" , "Seashore foam" , "Seaside froth" , "White foam of breaking waves" , "Ride waves - browse net" .)

I've seen this clue in The Globe and Mail.

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