/ Dictionary / Index U unthinkable: Meaning and Definition of Find definitions for: un•think•a•ble Pronunciation: (un-thing'ku-bul), [key] — adj. inconceivable; unimaginable: the unthinkable size of the universe. not to be considered; out of the question: Such a suggestion is unthinkable. —n. 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. See also: unthinkable (Thesaurus) unthink unthinking Related Content Daily Word Quiz: spectral Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language