Girl quiet in the morning (3)
I believe the answer is:
pam
'girl' is the definition.
'quiet in the morning' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano').
'in the morning' becomes 'am'.
'p'+'am'='PAM'
(Other definitions for pam that I've seen before include "- Ayres, English poet" , "Short girl's name" , "Female" .)