un·​known | \ ˌən-ˈnōn How to pronounce unknown (audio) \

Definition of unknown

 (Entry 1 of 2)

: not known or not well-known also : having an unknown value an unknown quantity



Definition of unknown (Entry 2 of 2)

1 : one that is not known or not well-known especially : a person who is little known (as to the public)
2 : something that requires discovery, identification, or clarification: such as
a : a symbol (such as x, y, or z) in a mathematical equation representing an unknown quantity
b : a specimen (as of bacteria or mixed chemicals) required to be identified as an exercise in appropriate laboratory techniques

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Synonyms for unknown

Synonyms: Adjective

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Examples of unknown in a Sentence

Adjective a disease of unknown cause Much remains unknown about his early life. Her music was previously unknown outside of Asia. An unknown number of cases go unreported. The victim's attacker was unknown to her. For some unknown reason, my computer crashed. a book of unknown poems Noun explorers venturing off into the unknown A fear of the unknown kept her from changing jobs. The director cast an unknown in the lead role. We're facing too many unknowns.
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Recent Examples on the Web: Adjective At such a point, general relativity is thought to give way to a more exact, as yet unknown, quantum-scale description of gravity. Quanta Magazine, "Black Hole Singularities Are as Inescapable as Expected," 2 Dec. 2019 Dutch police say the motive for the stabbing in The Hague remains unknown. Arkansas Online, "Dutch police arrest suspect in stabbing of 3 teens," 30 Nov. 2019 The extent of the problem with vape fluid containers across some 11,500 vape stores nationally remains unknown. Terry Demio, Cincinnati.com, "Vape juice can kill kids. A vaping law's slow rollout left them at risk of nicotine poison," 25 Nov. 2019 Perhaps this is why its particular array of symptoms, the cause of which was then unknown, inspired writers to assign a supernatural explanation, researchers recently reported. Fox News, "Bram Stoker's vampire victim shows 'textbook' leukemia symptoms," 22 Nov. 2019 And although the details of Swift’s Big Machine contract are unknown, this sort of restriction is part of long-standing record-label policy. Steve Knopper, Billboard, "Taylor Swift's Fight to Perform on the AMAs Is Less About the Show & More About How It's Watched," 18 Nov. 2019 Because the substance was unknown, the incident was labeled a level 2 hazmat situation, which means a larger response, according to Alkins. BostonGlobe.com, "Part of Summer Street in downtown Boston was closed Saturday morning in response to a level 2 hazmat situation after a steam leak left unknown debris on the street, according the Boston fire department.," 16 Nov. 2019 There is uncertainty around 0-8 Cincinnati’s biggest unknown, rookie quarterback Ryan Finley, who will make his first career start in place of Bengals veteran Andy Dalton. Jonas Shaffer, baltimoresun.com, "The Ravens beat the Bengals a month ago, but a rare rematch could be tricky: ‘They play out a lot differently’," 8 Nov. 2019 But the stories of how these communities became or stayed mostly white are often unknown, ignored or not fully told. Logan Jaffe, ProPublica, "Revisiting an American Town Where Black People Weren’t Welcome After Dark," 7 Nov. 2019 Recent Examples on the Web: Noun But even with a top Castleman specialist treating him, there were many unknowns. Ryan Prior, CNN, "This med student was given last rites before finding a treatment that saved his life. His method could help millions," 14 Sep. 2019 There are many unknowns about how nefarious actors may try to suppress the count by introducing doubt about the confidentiality of the census and how data is used. Bill Lambrecht, ExpressNews.com, "Advocates push Census Bureau to prepare for security breaches, disinformation ahead of 2020 count," 30 Aug. 2019 Crosby coach Jerry Prieto acknowledged that this year’s team will be young and that there are many unknowns going into the season but said that the team is not influenced at all by preseason magazine rankings. Elliott Lapin, Houston Chronicle, "Football: Dave Campbell’s magazine projects Crosby, Huffman to make playoffs," 11 July 2019 Palmer said that health care is complex and there are so many unknowns that an immediate, itemized cost list is not possible. Laura Hancock, cleveland.com, "Health care price transparency a sticking point in Ohio budget negotiations," 24 June 2019 While there are still many unknowns, scientists are excited about what other clues the jaw may hold for understanding human evolution in Asia. National Geographic, "Mysterious ancient human found on the ‘roof of the world’," 1 May 2019 It’s hard to imagine YouTube would lie about this, but at the same time, there are so many unknowns here that don’t really address the root of YouTubers’ worries. Patricia Hernandez, The Verge, "YouTube is failing its creators," 21 Sep. 2018 Frankly, there were too many unknowns to jump to conclusions about exactly what was going on initially. Samuel Axon, Ars Technica, "2018 15-inch MacBook Pro review: Better, faster, stronger?," 24 July 2018 Vaping is widely believed to be at least somewhat safer than traditional tobacco cigarettes, though there are still many unknowns. Scott Berson, miamiherald, "Teen tried vaping. Weeks later, she was on a breathing machine with 'wet lung,' study says | Miami Herald," 17 May 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'unknown.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of unknown


14th century, in the meaning defined above


1597, in the meaning defined at sense 1

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Time Traveler for unknown

Time Traveler

The first known use of unknown was in the 14th century

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Statistics for unknown

Last Updated

6 Dec 2019

Cite this Entry

“Unknown.” The Merriam-Webster.com Dictionary, Merriam-Webster Inc., https://www.merriam-webster.com/dictionary/unknown. Accessed 7 December 2019.

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More Definitions for unknown


How to pronounce unknown (audio)

English Language Learners Definition of unknown

 (Entry 1 of 2)

: not known
: not well-known : not famous



English Language Learners Definition of unknown (Entry 2 of 2)

: a place, situation, or thing that you do not know about or understand
: a person who is not famous or well-known
: something that is not known or not yet discovered


un·​known | \ ˌən-ˈnōn How to pronounce unknown (audio) \

Kids Definition of unknown

 (Entry 1 of 2)

: not known … it was cut all over with strange lines and figures that might be the letters of an unknown language.— C. S. Lewis, The Lion, the Witch and the Wardrobe



Kids Definition of unknown (Entry 2 of 2)

: one (as a quantity) that is unknown

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More from Merriam-Webster on unknown

Thesaurus: All synonyms and antonyms for unknown

Rhyming Dictionary: Words that rhyme with unknown

Spanish Central: Translation of unknown

Nglish: Translation of unknown for Spanish Speakers

Britannica English: Translation of unknown for Arabic Speakers

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