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Meaning of unthinkable

un•think•a•ble

Pronunciation: (un-thing'ku-bul), [key]
— adj.
  1. inconceivable; unimaginable: the unthinkable size of the universe.
  2. not to be considered; out of the question: Such a suggestion is unthinkable.
—n.
  1. something that cannot be conceived or imagined, as something too unusual, vague, or disagreeable: Today's unthinkables are tomorrow's realities.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.
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