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  1. not probable; unlikely to be true or to happen: Rain is improbable tonight.
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Origin of improbable

From the Latin word improbābilis, dating back to 1590–1600. See im-2, probable
Related formsim·prob·a·bly, adverbim·prob·a·ble·ness, nounsu·per·im·prob·a·ble, adjectivesu·per·im·prob·a·ble·ness, nounsu·per·im·prob·a·bly, adverb
Can be confusedimpossible impracticable impractical improbable

Synonyms for improbable

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Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for improbable

Contemporary Examples of improbable

Historical Examples of improbable

  • A thousand schemes were afloat in his mind about the future, of the most improbable kind.

    Life in London

    Edwin Hodder

  • But cold reason said that escape was improbable enough for me alone.

  • It is not improbable that a competitive examination, at this day, might have excluded him from the army.


    Samuel Smiles

  • This hypothesis was so improbable that Darwin himself was forced to recognize it.

  • That nude woman in the very midst of Paris—it's improbable.'

    His Masterpiece

    Emile Zola

British Dictionary definitions for improbable


  1. not likely or probable; doubtful; unlikely
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Derived Formsimprobability or improbableness, nounimprobably, adverb
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for improbable


1590s, from assimilated form of in- (1) "not, opposite of" + probable, or else from Latin improbabilis. Related: Improbably.

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Online Etymology Dictionary, © 2010 Douglas Harper