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

Officials said an initial investigation found that a Ford Fusion was stopped in one of the lanes for “unknown reasons” and a semi-truck struck it in the rear and then jackknifed.

From Washington Post

Around the 50-minute mark a jackknife plot turn sends it careering off-road, and it becomes an overburdened movie rather than a nimble one.

From Time

She cut it with Henry's jackknife into four quarters, and she and Henry took the two crusty ends themselves.

From Project Gutenberg

It was a rather battered jackknife, and Scattergood noticed that one blade had been broken off.

From Project Gutenberg

Mr. Blossom drew a jackknife from his pocket and began leisurely to sharpen a pencil.

From Project Gutenberg

Then he got up, jerked Mr. Blossom's old jackknife from the post where it had been abandoned, and pocketed it.

From Project Gutenberg

"I've heard tell you kin cut real gold like cheese," he said, and opened his jackknife.

From Project Gutenberg