Chorus voice (4)
I believe the answer is:
alto
'chorus voice' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for alto that I've seen before include "Voice part" , "The highest adult male singing voice" , "The highest adult male singing-voice" , "Second of four parts (in singing)" , "Singing voice between tenor and soprano" .)