Influential piece of music (12)
I believe the answer is:
instrumental
I believe this is a triple definition!
'influential' is the first definition.
(thesaurus)
'piece' is the second definition.
(I have seen 'piece of music' mean 'instrumental' so perhaps 'piece' could also mean 'instrumental')
'of' is a link.
'music' is the third definition.
(I've seen this before)
(Other definitions for instrumental that I've seen before include "Having some responsibility - not vocal" , "Piece of music without voices" , "Acting as a means; piece of music without vocals" , "doing without singers" , "Helpful; composition" .)