Rank or rating in this way given to instrument (8)
I believe the answer is:
absolute
'rank' is the definition.
(synonyms)
'rating in this way given to instrument' is the wordplay.
'rating' becomes 'ab' (both can mean a sailor).
'in this way' becomes 'so'.
'given to' means one lot of letters go next to another.
'instrument' becomes 'lute' (lute is a kind of instrument).
'ab'+'so'+'lute'='ABSOLUTE'
'or' acts as a link.
(Other definitions for absolute that I've seen before include "Sheer, total, not limited" , "Unlimited (power)" , "Rival" , "-273.15degC" , "Free from limits, power perhaps" .)