1. not definitely ascertainable or fixed, as in time of occurrence, number, dimensions, or quality.
  2. not confident, assured, or free from hesitancy: an uncertain smile.
  3. not clearly or precisely determined; indefinite; unknown: a manuscript of uncertain origin.
  4. vague; indistinct; not perfectly apprehended: an abstruse novel with uncertain themes.
  5. subject to change; variable; capricious; unstable: a person of uncertain opinions.
  6. ambiguous; unreliable; undependable: Her loyalties are uncertain.
  7. dependent on chance or unpredictable factors; doubtful; of unforeseeable outcome or effect.
  8. unsteady or flickering, as light; of changing intensity or quality.

Origin of uncertain

Middle English word dating back to 1250–1300; see origin at un-1, certain
Related formsun·cer·tain·ly, adverbun·cer·tain·ness, noun

Synonyms for uncertain

Synonym study

1. Uncertain, insecure, precarious imply a lack of predictability. That which is uncertain is doubtful or problematical; it often involves danger through an inability to predict or to place confidence in the unknown: The time of his arrival is uncertain. That which is insecure is not firm, stable, reliable, or safe, and hence is likely to give way, fail, or be overcome: an insecure foundation, footing, protection. Precarious suggests great susceptibility to failure, or exposure to imminent danger: a precarious means of existence.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for uncertainness


  1. not able to be accurately known or predictedthe issue is uncertain
  2. (when postpositive, often foll by of) not sure or confident (about)a man of uncertain opinion
  3. not precisely determined, established, or decideduncertain plans
  4. not to be depended upon; unreliablean uncertain vote
  5. liable to variation; changeablethe weather is uncertain
  6. in no uncertain terms
    1. unambiguously
    2. forcefully
Derived Formsuncertainly, adverbuncertainness, noun
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 uncertainness



c.1300, "of indeterminate time or occurrence," from un- (1) "not" + certain (adj.). Meaning "not fully confident" is recorded from late 14c. (implied in uncertainty). Related: Uncertainly.

Online Etymology Dictionary, © 2010 Douglas Harper

Idioms and Phrases with uncertainness


see in no uncertain terms.

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.