jack-knife

== English == === Alternative forms === jackknife === Etymology === (This etymology is missing or incomplete. Please add to it, or discuss it at the Etymology scriptorium.) === Pronunciation === === Noun === jack-knife (plural jack-knives) A compact folding knife. (diving) The front-dive pike, in which the body folds and unfolds. (sports) An abdominal exercise where knees and torso are raised from a lying position. (road transport, colloquial) A semi-trailer truck accident in which the vehicle mimics the closing of a jack-knife. (games) 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. Synonym: mumblety peg (statistics) Alternative spelling of jackknife. ==== Derived terms ==== jack-knife barber ==== Translations ==== ==== See also ==== === Verb === jack-knife (third-person singular simple present jack-knifes, present participle jack-knifing, simple past and past participle jack-knifed) 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. ==== Translations ====