Movement at sea is wonderful (5)
I believe the answer is:
swell
I believe this clue is a double definition.
'movement at sea' is the first definition.
(I've seen this before)
'is wonderful' is the second definition.
(swell can mean excellent)
(Other definitions for swell that I've seen before include "First class" , "Gentle sea movement" , "Puff up" , "Balloon - dandy" , "Heave of sea; expand" .)