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jack-knife (n.)[jack-knife 词源字典]: also jackknife, large pocket knife, 1711, probably American English, "perh[aps] associated with some sense of JACK sb.1, but compare jackleg knife" [OED]; see jack + knife (n.). Jackleg was a U.S. colloquial term of contempt from c. 1850. On another theory, so called because it originally was associated with sailors. As a kind of swimming dive, from 1922. As a type of tractor-trailer accident, 1966. Both from the notion of folding, as the knife does.[jack-knife etymology, jack-knife origin, 英语词源]
jack-knife (v.): 1776, "to stab," from jack-knife (n.). Intransitive meaning "to fold or bend" the body is said to date from the time of the American Civil War. The truck accident verbal sense is from 1949. Related: Jackknifed; jackknifing.