jackknife

1 of 2

noun

jack·​knife ˈjak-ˌnīf 

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

jackknife

2 of 2

verb

jackknifed; jackknifing; jackknifes

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

Verb

The truck jackknifed on the icy road.

Recent Examples on the Web

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

Word History

First Known Use

Noun

1683, in the meaning defined at sense 1

Verb

1886, in the meaning defined at intransitive sense 2

Kids 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