"A broken flute", I put in, "is useless" (6)
I believe the answer is:
futile
'useless' is the definition.
(similar in meaning)
'a broken flute i put in' is the wordplay.
'a broken' is an anagram indicator.
'put in' is an insertion indicator.
'flute' is an anagram of 'futle'.
'futle' going around 'i' is 'FUTILE'.
'is' acts as a link.
(Other definitions for futile that I've seen before include "Effectless" , "Useless, pointless" , "Useless, a waste of effort" , "Ineffective" , "Useless, producing no results" .)