Very high voice holding one girl back (9)
I believe the answer is:
altissimo
'very high' is the definition.
(musical term)
'voice holding one girl back' is the wordplay.
I cannot quite understand how this works, but
'one' could be 'o' (I've seen this in other clues) and 'o' is present in the answer.
'girl' could be 'issi' and 'issi' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for altissimo that I've seen before include "Very highly pitched" , "Very high musical pitch" , "one is almost dizzy" , "Very highly placed" .)