The mien of one who as an excellent right (3)
I believe the answer is:
air
'the mien of one who' is the definition.
'air' can be an answer for 'the mien' (I've seen this before). I'm not certain of the rest of the definition.
'excellent right' is the wordplay.
'excellent' becomes 'ai' (resembles 'A1', old-fashioned term for excellent).
'right' becomes 'r' (common abbreviation).
'ai'+'r'='AIR'
'as an' is the link.
Can you help me to learn more?
(Other definitions for air that I've seen before include "Publish" , "Gas mix surrounding the earth" , "Tune or aura" , "Means of travelling" , "Ventilate or give expression to" .)