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


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

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 Although, his jackknife-cannonball form could also use some polishing as well. Chris Kwiecinski, ajc, "Michigan’s Jim Harbaugh spends his bye week Saturday practicing his cannonball," 30 Sep. 2017 In a jackknife the trailer comes all the way around, takes both lanes, and crushes against the cab until the whole thing comes to a crashing stop at the bottom of the abyss or against the granite side of the Rockies. Longreads, "A High-End Mover Dishes on Truckstop Hierarchy, Rich People, and Moby Dick," 21 Sep. 2017 No weapon was found on Napier, although investigators discovered a jackknife and an ice pick-type tool stuck into the wall of the garage, not far from where Napier was first confronted. Jeff Mcdonald, sandiegouniontribune.com, "Oversight panel says deputies gave 3 different stories in 2014 fatal shooting," 27 July 2017 T. Christianson (@MSPPIO_SOUTH) January 10, 2017 SE MN very windy and fresh snow cause semis to jackknife. Tad Vezner, Twin Cities, "More snow makes for another lousy commute," 10 Jan. 2017 One photograph captured the image of a towheaded boy of about 3, stripping bark off a stick with a jackknife. Alice Gregory, New York Times, "Running Free in Germany’s Outdoor Preschools," 18 May 2017

Recent Examples on the Web: Verb

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

17 Nov 2018

Look-up Popularity

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 \
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

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