Note called out for a singer (5)
I believe the answer is:
tenor
'a singer' is the definition.
(tenor is a kind of singer)
'note called out' is the wordplay.
'note' becomes 'tenner' (a ten pound sterling bank note).
'called out' shows a homophone (sound like).
'tenner' is a homophone of 'TENOR'.
'for' acts as a link.
(Other definitions for tenor that I've seen before include "Voice classification of Jose Carreras" , "Higher male voice" , "Singer (one of three?)" , "Pavarotti, maybe" , "Vocal part" .)