A plucked instrument enthralling bishop -- so perfect (8)
I believe the answer is:
absolute
'perfect' is the definition.
('absolute' can be a synonym of 'perfect')
'a plucked instrument enthralling bishop so' is the wordplay.
'plucked instrument' becomes 'lute' (I've seen this before).
'enthralling' indicates putting letters inside.
'bishop' becomes 'b' (abbreviation used in chess).
'a'+'lute'='alute'
'b'+'so'='bso'
'alute' going around 'bso' is 'ABSOLUTE'.
(Other definitions for absolute that I've seen before include "-273.15degC" , "Total, utter" , "unrestricted by constitutional checks" , "rank" , "Complete or not limited" .)