A very rough sea; fun but dangerous (6)
I believe the answer is:
unsafe
'dangerous' is the definition.
(synonyms)
'a very rough sea fun' is the wordplay.
'sea fun' anagrams to 'UNSAFE'.
But, I'm unsure how the anagram is indicated.
'but' is the link.
Can you help me to learn more?
(Other definitions for unsafe that I've seen before include "Precarious" , "Unreliable" , "Hazardous" , "Dangerous - legally without basis" , "Not reliable, dangerous - perhaps a legal conviction" .)