1. folded sharply at an angle like a jackknife blade
Usage: past tense of jackknife
2. (of a truck and trailer) formed a sharp angle when the trailer swung around toward the cab
Usage: automotive

Examples

• The semi-truck jackknifed on the icy highway.
• He jackknifed his body to dive into the pool.
• The trailer jackknifed when the driver braked too hard.
• She jackknifed forward when the car stopped suddenly.
• The articulated bus jackknifed around the corner.
• The gymnast jackknifed in mid-air during her routine.