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
1
: to double up like a jackknife
jackknifed into a seat beside me, folding up his six feet eight—
Lady Bird Johnson
Lady Bird Johnson2
: to turn and form an angle of 90 degrees or less with each other
—used especially of a tractor-trailer combination
Examples of jackknife in a Sentence
Verb
The truck jackknifed on the icy road.
Recent Examples on the Web
Jacqueline Tempera, Women's Health, 28 Apr. 2023
Nissan says the SUVs have jackknife folding keys that may not stay fully open.
—CBS News, 28 Feb. 2023
Marina Johnson, The Courier-Journal, 25 Jan. 2024
The big rig jackknifed approximately 20 feet off the roadway and down an embankment, according to the CHP.
—Rick Hurd, The Mercury News, 18 July 2024
See all Example Sentences for jackknife 
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Noun
And the name of the game is squats: Pistol squats, goblet squats with weight, and jackknife crunches are all part of the usual regimen for Naomi.
—Jacqueline Tempera, Women's Health, 28 Apr. 2023
Nissan says the SUVs have jackknife folding keys that may not stay fully open.
—CBS News, 28 Feb. 2023
Verb
What to know 1:50 p.m.: All WB lanes on Watterson Expressway at Shelbyville Road closed after semi-truck crash
All westbound lanes near the 20-mile marker on Interstate 264 are closed after a tractor trailer jackknifed on the roadway Friday afternoon.
—Marina Johnson, The Courier-Journal, 25 Jan. 2024
The big rig jackknifed approximately 20 feet off the roadway and down an embankment, according to the CHP.
—Rick Hurd, The Mercury News, 18 July 2024
See all Example Sentences for jackknife
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Dictionary Entries Near jackknife
Cite this Entry
“Jackknife.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/jackknife. Accessed 26 Nov. 2024.
Copy CitationKids Definition
jackknife
1 of 2 noun
jack·knife
ˈjak-ˌnīf 
1
: a large strong pocketknife
2
: a dive in which the diver bends from the waist and touches the ankles before straightening out
jackknife
2 of 2 verb
: to double up like a jackknife
the trailer truck jackknifed
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