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[jak-nahyf] /ˈdʒækˌnaɪf/
noun, plural jackknives.
a large pocketknife.
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), jackknifed, jackknifing.
to bend or double over like a jackknife:
The prizefighter jackknifed and fell when he was hit in the stomach.
(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.
(in diving) to perform a jackknife.
to move rapidly at an abrupt angle.
verb (used with object), jackknifed, jackknifing.
to cause to jackknife:
The blow jackknifed the prizefighter.
to cut with a jackknife.
resembling a jackknife, as in its shape, function, or manner of opening and folding.
Origin of jackknife
1705-15, Americanism; jack1 (cf. jockteleg) + knife Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the Web for jackknife
Historical Examples
  • But he had no confidence in the flimsy birch bark; so he got out his jackknife and bade Billy get out his.

    A Busy Year at the Old Squire's Charles Asbury Stephens
  • Robert drew a jackknife from his pocket, and did as he was bidden.

    Brave and Bold Horatio Alger
  • The catch on the pantry window was loose, however, and Morrow managed to pry it open with his jackknife.

    The Crevice William John Burns and Isabel Ostrander
  • The black strips at the end of each nail, Martin pared off with his jackknife.

    Dust Mr. and Mrs. Haldeman-Julius
  • Then he pulled out his jackknife and felt its sharp edge with his thumb.

    The Tale of Timothy Turtle Arthur Scott Bailey
  • He took out his jackknife, and reaching over, severed the traces.

    Cap'n Eri Joseph Crosby Lincoln
  • The knees of Elliot doubled up under him like the blade of a jackknife.

    The Yukon Trail William MacLeod Raine
  • Them are his trousers I've on me and he gave me an oilskin and that jackknife.

    Ulysses James Joyce
  • Like a flash he pulled out his jackknife and opened the blade.

    The Putnam Hall Encampment Arthur M. Winfield
  • With his jackknife he cleaned the fish as best he could, and then broiled it on a green twig.

    Boys of The Fort Ralph Bonehill
British Dictionary definitions for jackknife


noun (pl) -knives
a knife with the blade pivoted to fold into a recess in the handle
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 (intransitive)
(of an articulated lorry) to go out of control in such a way that the trailer swings round at an angle to the cab
to make a jackknife dive
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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