/ ˈdʒæknaɪf; NAmE / noun , verb
■ noun
( pl. jack·knives / -naɪvz; NAmE /) a large knife with a folding blade
■ verb
[ v ] to form a V-shape. For example if a lorry / truck that is in two parts jackknifes , the driver loses control and the back part moves towards the front part.