Restrained having sat back and broken flute (8)
I believe the answer is:
tasteful
'restrained' is the definition.
(thesaurus)
'sat back and broken flute' is the wordplay.
'back' says the letters should be written backwards.
'and' means one lot of letters go next to another.
'broken' indicates anagramming the letters.
'sat' backwards is 'tas'.
'flute' anagrammed gives 'teful'.
'tas'+'teful'='TASTEFUL'
'having' acts as a link.
(Other definitions for tasteful that I've seen before include "with discrimination" , "Aesthetically pleasing" , "pleasantly entertaining" , "Discriminating" , "Free of tawdriness" .)