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

The Brent Spence was closed for 41 days, starting Nov. 11, 2020, after a semi-truck crashed into a truck that had jackknifed on the Brent Spence and set off a fire. —Patricia Gallagher Newberry, The Enquirer, 5 Dec. 2024

State troopers in northern Minnesota responded to several accidents, including tractor-trailers that jackknifed on Interstate 94 after the roadway became slippery from snow and ice. —Gqlshare, Hartford Courant, 20 Nov. 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