For the crossword clue “unalterable,” a very common 3‑letter answer is SET.

If your puzzle needs a different length, other frequent answers include:

  • FINAL
  • FIRM
  • FIXED
  • RIGID
  • PERMANENT
  • IMMUTABLE
  • UNCHANGEABLE

Match the answer to:

  • The required number of letters in the grid.
  • Any crossing letters you already have.