Of the movements of the sea (5)
I believe the answer is:
tidal
'of the movements of the sea' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for tidal that I've seen before include "Like the sea" , "Of sea, rising and falling" , "Of ebbs and flows" , "__ wave; tsunami" , "To do with movement of seas" .)