Origin of jackknife

1705–15, Americanism; jack1 (cf. jockteleg) + knife

Example sentences from the Web for jack-knife

British Dictionary definitions for jack-knife

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