Definition of "unalterable"

unalterable

adjective
comparative more unalterable, superlative most unalterable
1. Incapable of being altered, or of changing.
  Quotations
  People of unalterable ideas still insisted upon calling him "Sergeant" when they met him, which was in some degree owing to his having still retained the well-shaped moustache of his military days, and the soldierly bearing inseparable from his form.
  1874, Thomas Hardy, “Coming Home—A Cry”, in Far from the Madding Crowd. […], volume II, London: Smith, Elder & Co., […], pages 99–100
  ... every statute in the Bible and in the law books is an attempt to defeaat a law of God—in other words an unalterable and indestructible law of nature.
  c. 1909, Mark Twain, Letters from the Earth, Letter VIII
2. Irreversible, irrevocable.