jackknife

noun

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jack·knife | \ ˈjak-ˌnīf

Definition of jackknife

(Entry 1 of 2)

1 : a large strong pocketknife

2 : a dive executed headfirst in which the diver bends from the waist and touches the ankles while holding the knees unbent and then straightens out

jackknife

verb

jackknifed; jackknifing; jackknifes

Definition of jackknife (Entry 2 of 2)

intransitive verb

1 : to double up like a jackknife jackknifed into a seat beside me, folding up his six feet eight— Lady Bird Johnson

2 : to turn and form an angle of 90 degrees or less with each other —used especially of a tractor-trailer combination

transitive verb

1 : to cause to double up like a jackknife

2 : to cut with a jackknife

Examples of jackknife in a Sentence

Verb The truck jackknifed on the icy road.

Recent Examples on the Web: Noun The driver, a 41-year-old man from Mexico, lost control of the semi-truck in the rainy conditions, which caused the vehicle to jackknife and collide with the right shoulder wall, said Castro. — City News Service, San Diego Union-Tribune, 24 Dec. 2021 Not having to worry much about containment, his signature inside jackknife move took Cousins off his spots. — Ellis L. Williams, cleveland, 3 Oct. 2021 The final three moves are core crushers: the jackknife, boat pose hold, and push-up to opposite toe tap. — Christa Sgobba, SELF, 29 Apr. 2021 On the East Coast, from Canada to South Carolina, the Atlantic jackknife clam (also called a razor clam, but smaller than the Pacific variety) is sought in intertidal bays and estuaries. — Popular Science, 19 Oct. 2020 In one of his average workout classes, Curtis Adams will lead his group through a series of exercises, including jogging, jackknives and cardio boxing. — Olivia Lloyd, chicagotribune.com, 19 Sep. 2019 In one of his average workout classes, Curtis Adams will lead his group through a series of exercises, including jogging, jackknives and cardio boxing. — Olivia Lloyd, chicagotribune.com, 19 Sep. 2019 In one of his average workout classes, Curtis Adams will lead his group through a series of exercises, including jogging, jackknives and cardio boxing. — Olivia Lloyd, chicagotribune.com, 19 Sep. 2019 In one of his average workout classes, Curtis Adams will lead his group through a series of exercises, including jogging, jackknives and cardio boxing. — Olivia Lloyd, chicagotribune.com, 19 Sep. 2019 Recent Examples on the Web: Verb The driver of the commercial vehicle attempted to take evasive action which caused the truck-tractor and semi-trailer to jackknife across all the westbound lanes of the Interstate. — Kelli Smith, Dallas News, 16 Apr. 2021 The interesting-looking roofline flows back into a ducktail spoiler with slim taillights that jackknife down the quarter panel. — Connor Hoffman, Car and Driver, 9 Mar. 2021 The new model meets new, stronger crash-worthiness standards and is designed not to jackknife — guarding against the kind of derailment that killed eight people when Amtrak 188 took a turn too fast near Philadelphia in 2015. — CBS News, 11 June 2019 Oftentimes, jackknifing is a result of improper braking, poor road conditions or equipment failure. — Kimberly Rapanut, azcentral, 11 June 2018 The truck subsequently jackknifed and slid across all lanes of traffic, leading to the shutdown of the westbound side for a full eight hours. — Carol Cormaci, latimes.com, 9 Apr. 2018 On Twitter, State Police said tractor-trailers were jackknifed at various locations in central Massachusetts. — Laney Ruckstuhl And Elise Takahama, BostonGlobe.com, 13 Mar. 2018 Swiveling, jackknifing, raising her arms, and then crumpling over, Dunst has as much intensity as a Martha Graham dancer. — Amy Larocca, The Cut, 8 Aug. 2017 See More

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