Breaker (4)
(Other definitions for rock that I've seen before include "Large stone - type of music" , "Seaside sweet" , "musical genre?" , "lull baby to sleep?" , "See 17" .)
'breaker' is the definition.
(a wave 'breaks' on the shore)
This is all the clue.
(Other definitions for wave that I've seen before include "Undulate" , "Roller - breaker" , "Fasten; neckwear" , "roller, perhaps" , "Roller; a gesture" .)