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[im-prob-uh-buh l] /ɪmˈprɒb ə bəl/
not probable; unlikely to be true or to happen:
Rain is improbable tonight.
Origin of improbable
From the Latin word improbābilis, dating back to 1590-1600. See im-2, probable
Related forms
improbably, adverb
improbableness, noun
superimprobable, adjective
superimprobableness, noun
superimprobably, adverb
Can be confused
questionable, doubtful, implausible. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2017.
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Examples from the Web for improbably
Contemporary Examples
Historical Examples
  • Philip realized that William was the soul of the revolt and that without him it might not improbably have been put down.

  • It will be my duty to write to him in a few days, and not improbably with the same result.

    Luttrell Of Arran Charles James Lever
  • Not improbably the switch carried by the goat on this sign was originally a leek.

  • There would have been a scene, of course; and she, not improbably, might have told her father.

    Is He Popenjoy? Anthony Trollope
  • Certainly Homer is referring to an existing legend, and not improbably to a lay which in his time existed.

    The World of Homer Andrew Lang
British Dictionary definitions for improbably


not likely or probable; doubtful; unlikely
Derived Forms
improbability, improbableness, noun
improbably, 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
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Word Origin and History for improbably



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

Online Etymology Dictionary, © 2010 Douglas Harper
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