Origin of jackknife

1705–15, Americanism; jack1 (cf. jockteleg) + knife
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for jackknife

British Dictionary definitions for jackknife

jackknife
/ (ˈdʒækˌnaɪf) /

noun plural -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 (intr)

(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