jack-knife
noun
°A compact folding knife.
"He kept a jack-knife in his pocket for various tasks."
°The front-dive pike, in which the body folds and unfolds.
verb
°To fold in the middle, as a jackknife does.
°(colloquial) To cause a semi-trailer truck to fold like a jackknife in a traffic accident.
"Before I knew what was happening, I'd jack-knifed the rig like nobody's business."