COAL

Fossil fuel (4)

Solution has appeared in 2 crosswords (1 across and 1 down):

• Quick crossword No 16,314 — 2022-08-19 23:00:23
  20A: Fossil fuel (4)
• Quick crossword No 15,453 — 2019-11-16 00:00:22
  12D: Fossil fuel (4)