/ Dictionary / Index I improbable: Meaning and Definition of Find definitions for: im•prob•a•ble Pronunciation: (im-prob'u-bul), [key] — adj. not probable; unlikely to be true or to happen: Rain is improbable tonight. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: improbable (Thesaurus) improbability impromptu Related Content Daily Word Quiz: sequester Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language