Son not out, rotten sailor (6)
I believe the answer is:
sinbad
'sailor' is the definition.
(I've seen this before)
'son not out rotten' is the wordplay.
'son' becomes 's'.
'not out' becomes 'in' ('in' is the opposite to 'out').
'rotten' becomes 'bad' ('bad' can be similar in meaning to 'rotten').
's'+'in'+'bad'='SINBAD'
(Other definitions for sinbad that I've seen before include "Sailor of The thousand-and-one Nights" , "Sailor of Eastern tale" , "Pantomime sailor from the Arabian Nights (6)" , "Literary sailor" , "Legendary sailor from Arabian nights" .)