Like Schoenberg's music
I believe the answer is:
atonal
'like schoenberg's music' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for atonal that I've seen before include "(Of music) lacking key" , "(Of music) without key" , "Musically, having no established key" , "Not in a key (mus.)" , "Unaccented" .)