A little over half of audience riotously cheers (5)
I believe the answer is:
adieu
'riotously cheers' is the definition.
'adieu' can be an answer for 'cheers' (I've seen this before). I am unsure of the 'riotously' bit.
'a little over half of audience' is the wordplay.
'little over half of audience' becomes 'dieu' (I can't explain this - if you can you should believe this answer much more).
'a'+'dieu'='ADIEU'
(Other definitions for adieu that I've seen before include "cheers" , "A valediction" , "12 Down" , "Farewell, ami!" , "So long abroad" .)