Female soldier with old piece of music (6)
I believe the answer is:
adagio
'piece of music' is the definition.
(adagio is a kind of piece of music)
'female soldier with old' is the wordplay.
'female' becomes 'ada' (I've seen this in other clues).
'soldier' becomes 'GI' (GI can mean a US soldier).
'with' is a charade indicator (letters next to each other).
'old' becomes 'o' (abbreviation).
'ada'+'gi'+'o'='ADAGIO'
(Other definitions for adagio that I've seen before include "going slowly in work" , "Slowly and graceful, in music" , "leisurely movement" , "Slow musical passage" , "Movement in slow time" .)