Dandy waves at sea (5)
I believe the answer is:
swell
I believe this is a triple definition!
'dandy' is the first definition.
(both can informally mean excellent or satisfactory)
'waves' is the second definition.
(I've seen this before)
'at' is a link.
'sea' is the third definition.
(thesaurus)
(Other definitions for swell that I've seen before include "Gentle sea movement" , "Expand abnormally" , "'Increase in size, number etc (5)'" , "Bulge; a nob" , "organ feature" .)