Fictional mariner with a vice. Rotten (6)
I believe the answer is:
sinbad
'fictional mariner' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'with a vice rotten' is the wordplay.
'with' is a charade indicator (letters next to each other).
'a vice' becomes 'sin'.
'rotten' becomes 'bad' (similar in meaning).
'sin' next to 'bad' is 'SINBAD'.
Can you help me to learn more?
(Other definitions for sinbad that I've seen before include "Adventurous sailor of Arabian Nights or pantomime" , "Arabian Nights sailor who made seven voyages" , "The 1001 Nights sailor" , "Pantomime sailor from the Arabian Nights (6)" , "Literary sailor" .)