Sailor ruined date and subsided (6)
I believe the answer is:
abated
'subsided' is the definition.
(I've seen this before)
'sailor ruined date' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'ruined' indicates anagramming the letters.
'date' anagrammed gives 'ated'.
'ab'+'ated'='ABATED'
'and' acts as a link.
(Other definitions for abated that I've seen before include "Lowered" , "Subsided or decreased like storm" , "reduced" , "Eased" , "Relaxed" .)