I. ˈjack-knife1 noun (
plural jack-knives)
[countable]1. a knife with a blade that folds into its handle
2. a
dive in which you bend at the waist when you are in the air
[TahlilGaran] Dictionary of Contemporary English ▲
II. jack-knife2 verb [intransitive] if a large vehicle with two parts jack-knifes, it slides out of control and the back part swings towards the front part:
The truck skidded on the ice and jack-knifed. [TahlilGaran] Dictionary of Contemporary English ▲