Pretentious note on European Union party (6)
I believe the answer is:
pseudo
'pretentious' is the definition.
'note on european union party' is the wordplay.
'note' becomes 'ps' (PS is an example**).
'on' is a charade indicator (letters next to each other).
'european union' becomes 'eu'.
'party' becomes 'do' (do is a kind of party).
'ps'+'eu'+'do'='PSEUDO'
(Other definitions for pseudo that I've seen before include "O dupes! being false and insincere" , "Dose up (anag.); pretentious" , "Prefix for fake" , "Does up, looking phoney" , "Ersatz" .)