jackknife

noun jack·knife \ ˈjak-ˌnīf \

Updated on: 25 Feb 2018

Definition of jackknife

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

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Recent Examples of jackknife from the Web

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
Meanwhile, deadbugs, jackknives, ab-wheel rollouts, and boat pose variations will hit both portions.

— k. aleisha fetters, SELF, "Why It’s So Hard to Work Your Lower Abs," 4 July 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.

First Known Use of jackknife

1711

jackknife

verb

Definition of jackknife

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

See jackknife defined for English-language learners

Examples of jackknife in a Sentence

The truck jackknifed on the icy road.

Recent Examples of jackknife from the Web

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