Lively riptides at sea (8)
I believe the answer is:
spirited
'lively' is the definition.
(associated in meaning)
'riptides at sea' is the wordplay.
'at sea' is an anagram indicator.
'riptides' anagrammed gives 'SPIRITED'.
(Other definitions for spirited that I've seen before include "with brio" , "Full of beans" , "Lively and brave" , "Secretly transported" , "Mettlesome" .)