1. a large folding knife with one or more blades
2. a dive in which the diver bends at the waist and touches the toes before straightening out
Usage: sports

1. to fold or bend sharply at the middle like a jackknife
2. to turn or swing around quickly

Examples

• He pulled out his jackknife to cut the rope.
• The camper used a jackknife to prepare dinner.
• She performed a perfect jackknife dive from the high board.
• The truck jackknifed on the icy highway.
• The trailer jackknifed when the driver braked suddenly.
• His body jackknifed in pain.
• The car jackknifed around the corner.