ATONAL

Not written in a key (6)

Solution has appeared in 2 crosswords (2 across and 0 down):

• Quick crossword No 16,574 — 2023-06-19 23:00:25
  13A: (Musically) lacking harmony (6)
• Quick crossword No 15,916 — 2021-05-11 23:00:29
  7A: Not written in a key (6)