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 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, "14 wild edibles you can pull right out of the ocean," 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, "Exercise instructor redefines fitness for seniors," 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, "Exercise instructor redefines fitness for seniors," 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, "Exercise instructor redefines fitness for seniors," 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, "Exercise instructor redefines fitness for seniors," 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, "Exercise instructor redefines fitness for seniors," 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, "Exercise instructor redefines fitness for seniors," 19 Sep. 2019 The fourth vehicle then ran into a semi-truck, which caused the semi to jackknife and slam into the center median. — Dallas News, "Wrong-way driver in deadly Duncanville crash gets life sentence," 23 Aug. 2019 Recent Examples on the Web: Verb 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, "Inside Amtrak's next-generation Acela train: "Wi-Fi, craft beers and reliable schedules"," 11 June 2019 Oftentimes, jackknifing is a result of improper braking, poor road conditions or equipment failure. — Kimberly Rapanut, azcentral, "Loop 101 WB at Hayden closed in Scottsdale after semitruck jackknifes," 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, "La Cañada History: Viper collides with big rig, shuts down 210 Freeway for 8 hours," 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, "Treacherous roadways cause at least 9 tractor-trailer crashes," 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, "Queen of the Wood Nymphs," 8 Aug. 2017

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.