Singer sounding note (5)
I believe the answer is:
tenor
'singer' is the definition.
(tenor is a kind of singer)
'sounding note' is the wordplay.
'sounding' shows a homophone (sound like).
'note' becomes 'tenner' (a tenner is a 10 pound note).
'tenner' is a homophone of 'TENOR'.
(Other definitions for tenor that I've seen before include "General drift or meaning" , "Singer; drift" , "Highest male voice" , "General meaning of a male voice" , "character" .)