EIGHT

Oxygen's atomic number (5)

Solution has appeared in 4 crosswords (2 across and 2 down):

• Quick crossword No 16,080 — 2021-11-19 00:00:19
  9A: ___ Days a Week, 1964 Beatles song (5)
• Quick crossword No 15,647 — 2020-06-30 23:00:06
  19D: Rowing crew (5)
• Quick crossword No 15,430 — 2019-10-20 23:00:10
  22A: Number etched by a skater? (5)
• Quick crossword No 15,289 — 2019-05-08 23:00:24
  18D: Oxygen's atomic number (5)