jackknife

American  

[jak-nahyf] / ˈdʒækˌnaɪf /

noun

plural

jackknives

1. a large pocketknife.

2. Fancy Diving. a dive in which the diver bends in midair to touch the toes, keeping the legs straight, and then straightens out.

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verb (used without object)

jackknifed, jackknifing

1. to bend or double over like a jackknife.

   The prizefighter jackknifed and fell when he was hit in the stomach.

2. (of a trailer truck) to have the cab and trailer swivel at the linkage until they form a V shape, as the result of an abrupt stop or accident.

3. (in diving) to perform a jackknife.

4. to move rapidly at an abrupt angle.

verb (used with object)

jackknifed, jackknifing

1. to cause to jackknife.

   The blow jackknifed the prizefighter.

2. to cut with a jackknife.

adjective

1. resembling a jackknife, as in its shape, function, or manner of opening and folding.

jackknife British  

/ ˈdʒækˌnaɪf /

noun

1. a knife with the blade pivoted to fold into a recess in the handle

2. a former name for a type of dive in which the diver bends at the waist in midair, with his legs straight and his hands touching his feet, finally straightening out and entering the water headfirst: forward pike dive

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verb

1. (of an articulated lorry) to go out of control in such a way that the trailer swings round at an angle to the cab

2. to make a jackknife dive

Etymology

Origin of jackknife

1705–15, jack ¹ ( jockteleg ) + knife

Example Sentences

The keys for these models are jackknife fobs, wherein the metal blade of the key can fold in and out of the plastic fob.

From Washington Times • Mar. 1, 2023

The officer had gotten out of a vehicle after seeing a semi-trailer jackknife on the road and the patrol car was struck by a passenger car.

From Seattle Times • Nov. 10, 2022

But somehow, it’s entirely too easy to oversteer and jackknife, or to understeer and do an embarrassingly crooked parking job.

From Washington Post • Sep. 23, 2021

Digging with a garden shovel and jackknife, Kathy Wankel unearthed a complete T rex arm.

From The Guardian • Jan. 1, 2019

He took a jackknife out of his pocket and dug a little scoop of dirt out of one of the tracks.

From "Elijah of Buxton" by Christopher Paul Curtis