Note the listener's mood (6)
I believe the answer is:
tenner
'note' is the definition.
(a tenner is a 10 pound note)
'the listener's mood' is the wordplay.
'the listener's' shows a homophone (sound like) (how the word might sound to a listener).
'mood' becomes 'tenor' (both can mean a general meaning or tone).
'tenor' sounds like 'TENNER'.
(Other definitions for tenner that I've seen before include "Cash note" , "sounded by Peter Pears" , "Heard bell" , "British banknote" , "Bank note" .)