Courtesy seeing drunk English in gang (9)
I believe the answer is:
politesse
'courtesy' is the definition.
(politesse is a kind of courtesy)
'drunk english in gang' is the wordplay.
'drunk english' becomes 'lite' (I can't justify this - if you can you should give a lot more credence to this answer).
'in' means one lot of letters goes inside another.
'gang' becomes 'posse' (I've seen this in another clue).
'lite' placed into 'posse' is 'POLITESSE'.
'seeing' is the link.
Can you help me to learn more?
(Other definitions for politesse that I've seen before include "Chivalry" , "formal courtesy" , "Etiquette" .)