jack·​knife | \ ˈjak-ˌnīf How to pronounce jackknife (audio) \

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


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


The truck jackknifed on the icy road.

Recent Examples on the Web: Noun

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 The suspect stabbed the victim with a jackknife at the Temple Street YWCA at about 6:40 p.m., Cambridge police spokesman Jeremy Warnick said in an e-mail. Adam Sennott, BostonGlobe.com, "Cambridge police search for suspect in fitness class stabbing," 21 Aug. 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, sun-sentinel.com, "Exercise instructor redefines fitness for seniors," 1 Aug. 2019 Police found Flick’s 3 ½ inch jackknife in the living room. Wendy Grossman Kantor, PEOPLE.com, "What to Know About Albert Flick, the 77-Year-Old Murderer Deemed 'Too Old' to Be Violent," 19 July 2019 In his video, Kirsch walks viewers through hanging knee raises, a medicine ball spiderman, jackknives, and a medicine ball slam. SELF, "A Quick Core-Burning Workout From Jennifer Lopez's Trainer," 26 Oct. 2018 All new power ottomans and jackknife seats will complement two-tone high-end cabinetry, and plush diamond-stiched seating. Megan Barber, Curbed, "This limited edition Airstream touring coach goes all in on luxury," 5 Oct. 2018 John Paul Vitruk, 64, was driving south on Highway 169 with a loaded U-HAUL trailer attached to his pickup truck when the truck hit an icy area on the road, causing the trailer to jackknife, said Lee County Coroner Bill Harris. Anna Beahm, AL.com, "Auburn man killed after wreck on icy highway in Lee County," 19 Jan. 2018 The extremely limited-run beer is limited to 200 bottles, sold as survival kits that include a solar blanket, paracord, and Swiss Army jackknife. Matt Allyn, Popular Mechanics, "Creating the Perfect Beer for the End of the World," 5 Jan. 2018

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.

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First Known Use of jackknife


1683, in the meaning defined at sense 1


1886, in the meaning defined at intransitive sense 2

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Statistics for jackknife

Last Updated

8 Sep 2019

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Time Traveler for jackknife

The first known use of jackknife was in 1683

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More Definitions for jackknife



English Language Learners Definition of jackknife

 (Entry 1 of 2)

: a small knife that has a folding blade
: a dive in which you bend from the waist and touch your ankles and then straighten out



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

: to bend in the middle like a folding jackknife especially, of a large truck : to have the back part slide out of control toward the front part


jack·​knife | \ ˈjak-ˌnīf How to pronounce jackknife (audio) \
plural jackknives\ -​ˌnīvz \

Kids Definition of jackknife

 (Entry 1 of 2)

: a knife that has a folding blade or blades and can be put in a pocket


jackknifed; jackknifing

Kids Definition of jackknife (Entry 2 of 2)

: to double up like a jackknife

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More from Merriam-Webster on jackknife

Rhyming Dictionary: Words that rhyme with jackknife

Spanish Central: Translation of jackknife

Nglish: Translation of jackknife for Spanish Speakers

Britannica English: Translation of jackknife for Arabic Speakers

Comments on jackknife

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