A very quiet song turned to use (7)
I believe the answer is:
applied
'turned to use' is the definition.
I can't judge whether this definition defines the answer.
'a very quiet song' is the wordplay.
'very quiet' becomes 'pp' (musical abbreviation for pianissimo).
'song' becomes 'lied' (type of German song).
'a'+'pp'+'lied'='APPLIED'
Can you help me to learn more?
(Other definitions for applied that I've seen before include "sort of maths" , "Was relevant" , "put to practical use" , "Type of science" , "Employed" .)