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

Cooler heads prevailed, and Ospreay transitioned from a jackknife to a Style Clash for a nearfall. — Alfred Konuwa, Forbes.com, 12 Apr. 2026

Spud led in points after two rounds with a repertoire that included 360-degree jams; a reverse double-pump; a straight-ahead double, and a jackknife. — Kevin Sherrington feb. 10, Dallas Morning News, 10 Feb. 2026

Verb

The semi- truck then jackknifed and slid from the right lane to the left, causing a collision with three other passenger cars, DPS officials have said. — Shambhavi Rimal, Fort Worth Star-Telegram, 25 June 2026

Video from the scene shows a semi truck jackknifed into a barrier on the expressway. — Elyssa Kaufman, CBS News, 23 Apr. 2026

Word History

First Known Use

Noun

1683, in the meaning defined at sense 1

Verb

1886, in the meaning defined at intransitive sense 2

Rhymes for jackknife

• alewife
• birdlife
• folklife
• housewife
• midlife
• midwife
• nightlife
• penknife
• wildlife
• afterlife
• pocketknife
• knife

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