noun
A compact folding knife.
The front-dive pike, in which the body folds and unfolds.
(colloquial) A semi-trailer truck accident in which the vehicle mimics the closing of a jack-knife.
A game of skill played with a pocket knife in which participants try to throw or flip the knife to stick upright in the ground at specified points or areas; mumblety-peg.
(statistics) Alternative spelling of jackknife.
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.