IMMUNE

Invulnerable (6)

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

• Quick crossword No 15,857 — 2021-03-04 00:00:31
  13A: Secure against (6)
• Quick crossword No 15,208 — 2019-02-04 00:00:15
  12A: Invulnerable (6)