Unqualified sailor thus has instrument (8)
I believe the answer is:
absolute
'unqualified' is the definition.
('absolute' can be similar in meaning to 'unqualified')
'sailor thus has instrument' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'thus' becomes 'so' ('so' can be a synonym of 'thus').
'has' means one lot of letters go next to another.
'instrument' becomes 'lute' (lute is a kind of instrument).
'ab'+'so'+'lute'='ABSOLUTE'
(Other definitions for absolute that I've seen before include "Sheer, utter or not limited" , "Literary captain" , "Not subject to limitation" , "Complete - unlimited" , "No strings attached" .)