Docile and quiet subject (7)
I believe the answer is:
pliable
'docile' is the definition.
(thesaurus)
'quiet subject' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano').
'subject' becomes 'liable'.
'p'+'liable'='PLIABLE'
'and' is the link.
(Other definitions for pliable that I've seen before include "Easily bent" , "Flexible" , "Ductile" , "accommodating" , "Elastic" .)