Light up seaside resort for the audience (8)
I believe the answer is:
brighten
'light up' is the definition.
(synonyms)
'seaside resort for the audience' is the wordplay.
'seaside resort' becomes 'Brighton'.
'for the audience' shows a homophone (sound like) (how an audience might hear it).
'brighton' sounds like 'BRIGHTEN'.
(Other definitions for brighten that I've seen before include "Provide illuminations" , "Liven up" , "Cheer up; clear up" , "Illuminate, cheer up" , "Berthing (anag.)" .)