Gallant British party (5)
I believe the answer is:
brave
'gallant' is the definition.
(similar in meaning)
'british party' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'party' becomes 'rave' (type of dance party).
'b'+'rave'='BRAVE'
(Other definitions for brave that I've seen before include "Plucky" , "Defy" , "Heroic, valiant" , "Indian warrior" , "bottle?" .)