unalterable

un- +‎ alterable

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unalterable (comparative more unalterable, superlative most unalterable)

1. Incapable of being altered, or of changing.
   • 1874, Thomas Hardy, “Coming Home—A Cry”, in Far from the Madding Crowd. […], volume II, London: Smith, Elder & Co., […], →OCLC, pages 99–100:

     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.

   • c. 1909, Mark Twain, Letters from the Earth, Letter VIII:

     ... 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.

2. Irreversible, irrevocable.

• inalterable

• alterable

• unalterably

• unalertable, unrelatable