Pizzicato presumably not mastered (7)
I believe the answer is:
unbowed
'pizzicato presumably not mastered' is the definition.
The answer and definition are not the same part of speech. However, adjectives and past participle verbs occasionally define each other.
'not mastered' is the wordplay.
'not' becomes 'un' (prefix meaning 'not').
'mastered' becomes 'bowed' (I am not sure about this - if you are sure you should believe this answer much more).
'un'+'bowed'='UNBOWED'
Can you help me to learn more?
(Other definitions for unbowed that I've seen before include "pizzicato?" , "Not defeated" , "defiant?" , "Not like Cupid" , "Not having submitted to pressure" .)