jackknife

[ jak-nahyf ]

noun

, plural jack·knives.

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.

verb (used without object)

, jack·knifed, jack·knif·ing.

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)

, jack·knifed, jack·knif·ing.

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

/ 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

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

Word History and Origins

Origin of jackknife¹

1705–15, Americanism; jack ¹ ( jockteleg ) + knife

Example Sentences

The episode later reveals that a jackknifed big rig unleashed 22 million killer bees into L.A. when it crashed on the 4th Street Bridge.

From Los Angeles Times

Photos and video of the scene showed one carriage jackknifed several meters into the air above a badly mangled cargo train.

From Seattle Times

On Interstate 80 over the Sierra on Friday, multiple vehicles spun out and a big rig jackknifed.

From Los Angeles Times

Parts of Interstate 80 between Des Moines and Iowa City were repeatedly snagged overnight by jackknifed tractor-trailers and multiple-car pileups, the Department of Transportation reported.

From New York Times

Trucks jackknifed in the snow, blocking highways, as drivers reported taking hours to complete short trips while others were forced to find a place to stay along their routes or in their vehicles.

From Seattle Times