Ludicrous rhetoric around opening of serenade for singer (9)
I believe the answer is:
chorister
'for singer' is the definition.
(singer in a choir)
'ludicrous rhetoric around opening of serenade' is the wordplay.
'ludicrous' is an anagram indicator (a ludicrous spelling).
'around' is an insertion indicator.
'opening of' says to take the initial letters.
The initial letter of 'serenade' is 's'.
'rhetoric' with letters rearranged gives 'choriter'.
'choriter' enclosing 's' is 'CHORISTER'.
(Other definitions for chorister that I've seen before include "Choir member" , "Church, cathedral singer" , "Choirboy or girl" , "Boy in church" , "Boy singing" .)