■ noun ( plural jackknives )
1》 a large knife with a folding blade.
2》 a dive in which the body is bent at the waist and then straightened.
■ verb ( ~s , jackknifing , ~d )
1》 move (one's body) into a bent or doubled-up position.
↘(of a diver) perform a ~.
2》 (of an articulated vehicle) bend into a V-shape in an uncontrolled skidding movement.