jackknife
Americannoun
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a large pocketknife.
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Fancy Diving. a dive in which the diver bends in midair to touch the toes, keeping the legs straight, and then straightens out.
verb (used without object)
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to bend or double over like a jackknife.
The prizefighter jackknifed and fell when he was hit in the stomach.
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(of a trailer truck) to have the cab and trailer swivel at the linkage until they form a V shape, as the result of an abrupt stop or accident.
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(in diving) to perform a jackknife.
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to move rapidly at an abrupt angle.
verb (used with object)
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to cause to jackknife.
The blow jackknifed the prizefighter.
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to cut with a jackknife.
adjective
noun
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a knife with the blade pivoted to fold into a recess in the handle
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a former name for a type of dive in which the diver bends at the waist in midair, with his legs straight and his hands touching his feet, finally straightening out and entering the water headfirst: forward pike dive
verb
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(of an articulated lorry) to go out of control in such a way that the trailer swings round at an angle to the cab
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to make a jackknife dive
Other Word Forms
Inflected Forms
Nouns
Participles
Conjugated Forms
Present
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jackknifesimple
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jackknifessimple
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have jackknifedperfect
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has jackknifedperfect
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am jackknifingprogressive
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are jackknifingprogressive
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is jackknifingprogressive
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have been jackknifingperfect progressive
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has been jackknifingperfect progressive
Past
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jackknifedsimple
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had jackknifedperfect
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was jackknifingprogressive
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were jackknifingprogressive
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had been jackknifingperfect progressive
Future
Etymology
Origin of jackknife
Explanation
A knife with a blade that folds closed is called a jackknife. Most jackknives are compact enough to fit in a pocket, but we don't suggest your taking one to school. Another name for a jackknife is a pocketknife. Some jackknives have several different blades, all of which fold tidily (and safely) into the body of the knife, while others unfold to reveal a single blade. The bend of a jackknife inspired the name of the dive also called the jackknife, in which the diver's body folds into a V shape and then straightens out before the diver hits the water.
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
See Examples For:
The keys for these models are jackknife fobs, wherein the metal blade of the key can fold in and out of the plastic fob.
From Washington Times ● Mar. 1, 2023
The officer had gotten out of a vehicle after seeing a semi-trailer jackknife on the road and the patrol car was struck by a passenger car.
From Seattle Times ● Nov. 10, 2022
“That stretch of Virginia is so brittle that all it takes is a couple semis to jackknife and you shut down the main north-south artery along the Eastern Seaboard,” Ali said.
From Washington Post ● Jan. 5, 2022
Digging with a garden shovel and jackknife, Kathy Wankel unearthed a complete T rex arm.
From The Guardian ● Jan. 1, 2019
She asked the salesman to put everything into the canvas bag, except the jackknife.
From "Homecoming" by Cynthia Voigt
The catalog explains how Mr. Donati, a native of Milan, traveled in the American Southwest and Hudson Bay in the 1930s and traded European pheasant feathers, beads and jackknives for Indian artwork.
From New York Times ● May 6, 2010
After that, it was no trouble to win the National A.A.U. high & low-board championships with comparatively easy jackknives and gainers.
From Time Magazine Archive
Boys rolled marbles and obtained jackknives as they became older.
From Time Magazine Archive
He reports he performed the movie's swan dives and jackknives in "all but a fraction of a shot."
From Time Magazine Archive
He wanted to sit with them on curbstones and compare the sharpness of jackknives, the distance and arcs of spitting.
From "The Bluest Eye" by Toni Morrison
It jackknifes its sleek body and leaps out of my hand, scurrying off into the landscaping.
From Salon ● Jun. 15, 2019
“The problem is when a tractor-trailer jackknifes, it’s not like a Honda Accord, — it takes out the entire roadway,” he said.
From Washington Post ● Mar. 21, 2018
You may not be able to perform as many jackknifes, and that's fine.
From Los Angeles Times ● Sep. 5, 2014
Here, the cities of Florence and Muscle Shoals flank opposite sides of the Tennessee River just before it jackknifes back up into the state from whence it came.
From Southern Living ● Dec. 25, 2012
Legg not only jackknifes over eleven barrels but also leaps through a revolving, flaming ring.
From Time Magazine Archive
The episode later reveals that a jackknifed big rig unleashed 22 million killer bees into L.A. when it crashed on the 4th Street Bridge.
From Los Angeles Times ● Oct. 10, 2024
Parts of Interstate 80 between Des Moines and Iowa City were repeatedly snagged overnight by jackknifed tractor-trailers and multiple-car pileups, the Department of Transportation reported.
From New York Times ● Jan. 12, 2024
Four lorries have jackknifed in an eight-vehicle crash, causing major delays on a main road through Essex.
From BBC ● Mar. 30, 2023
Andreas Alikaniotis, a 20-year-old survivor, described how he and fellow students escaped from a jackknifed train car as the fire approached, smashing windows and throwing luggage outside to use as a makeshift landing pad.
From Seattle Times ● Mar. 2, 2023
We finally pass a jackknifed truck and get back up to speed, but Radar calculates in his head that we’ll need to average seventy-seven from here to Agloe.
From "Paper Towns" by John Green
At least 30 cars idling in the bike lane for unspecified reasons—hazard lights on—forcing me to maintain forward momentum by jackknifing into the busy thoroughfare.
From Slate ● Jun. 21, 2023
Within moments, police said more tractor trailers were jackknifing behind it.
From Washington Post ● Jan. 8, 2022
We know we cannot throw 95 miles an hour, or make the pivot on a double play with a runner bearing down, or square up a jackknifing curveball with a season on the line.
From New York Times ● Jun. 2, 2012
A look at Newser's home page on Monday morning compels with all the sick attraction exerted by a semi jackknifing across the interstate, setting in motion a 20-car pileup.
From Salon ● Apr. 5, 2010
I wedged my body down through the nearly solid sea of coils, forcing my legs deep into the cockpit and jackknifing my knees so that my upper body swung downward and inward.
From "Flying to the Moon: An Astronaut's Story" by Michael Collins
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
