The finale sounds like Sibelius (6)
I believe the answer is:
finish
'the finale' is the definition.
(synonyms)
'sounds like sibelius' is the wordplay.
'sounds' shows a homophone (sound like).
'like sibelius' becomes 'finnish' (I've seen this in another clue).
'finnish' is a homophone of 'FINISH'.
(Other definitions for finish that I've seen before include "End, complete" , "Terminate, conclude" , "Deal with" , "Conclude, stop" , "End, conclusion" .)