Adult whistled in audition (4)
I believe the answer is:
blue
'adult' is the definition.
(I know that adult can be written as blue)
'whistled in audition' is the wordplay.
'whistled' becomes 'blew' (I've seen this in another clue).
'in audition' shows a homophone (sound like) (audition can mean hearing).
'blew' is a homophone of 'BLUE'.
(Other definitions for blue that I've seen before include "This could be royal or navy" , "Glum, sad" , "Spend all at once - colour" , "ball at snooker" , "Woodland flower" .)