Fun sea travel is hazardous (6)
I believe the answer is:
unsafe
'hazardous' is the definition.
(similar in meaning)
'fun sea travel' is the wordplay.
'travel' is an anagram indicator (I've seen 'travels' mean this).
'fun'+'sea'='funsea'
'funsea' is an anagram of 'UNSAFE'.
'is' is the link.
(Other definitions for unsafe that I've seen before include "Precarious" , "Not reliable, dangerous - perhaps a legal conviction" , "Perilous" , "Dangerous, insecure" , "Unreliable" .)