Unkeyed, as some compositions (6)
I believe the answer is:
atonal
'unkeyed as some compositions' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for atonal that I've seen before include "(Of music) without key" , "Keyless" , "(Of music) not in any key or mode" , "Describes music not written in a particular key" , "Lacking traditional musical tone structure" .)