jackknife

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

The truck jackknifed on the icy road.

Recent Examples on the Web

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

Sunday, the Minnesota State Patrol reported three injury crashes, 68 property damage crashes, 177 vehicles off the road, nine spinouts and seven jackknifed semis. —Pioneer Press, Twin Cities, 15 Mar. 2026

The crash involved one semitruck that jackknifed across the highway and no one was injured, Trooper Gabriel Moltrer said. —Katie Langford, Denver Post, 8 Jan. 2026

Thomas Paine, 71, of Johnson Creek was killed in the crash after a semi-tractor trailer driver lost control, jackknifed and veered into opposite lanes, according to a Dec. 2 news release from the Sheriff's Office. —Claudia Levens, jsonline.com, 4 Dec. 2025

Word History

First Known Use

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