Stuck up American friend's nickname (3)
I believe the answer is:
dub
'nickname' is the definition.
(synonyms)
'stuck up american friend's' is the wordplay.
'stuck up' is a reversal indicator.
'american friend' becomes 'bud' (US term for friend).
'bud' backwards is 'DUB'.
(Other definitions for dub that I've seen before include "Add sound effects or music" , "Add a soundtrack in a different language" , "Ennoble" , "Add soundtrack to film in another language" , "Knight (someone) with a sword" .)