/jak"nuyf'/ , n. , pl. jackknives , v. , jackknifed, jackknifing , adj.
n.
1. a large pocketknife.
2. Fancy Diving. a dive in which the diver bends in midair to touch the toes, keeping the legs straight, and then straightens out.
v.i.
3. to bend or double over like a jackknife: The prizefighter jackknifed and fell when he was hit in the stomach.
4. (of a trailer truck) to have the cab and trailer swivel at the linkage until they form a V shape, as the result of an abrupt stop or accident.
5. (in diving) to perform a jackknife.
6. to move rapidly at an abrupt angle.
v.t.
7. to cause to jackknife: The blow jackknifed the prizefighter.
8. to cut with a jackknife.
adj.
9. resembling a jackknife, as in its shape, function, or manner of opening and folding.
[ 1705-15, Amer.; JACK 1 (cf. JOCKTELEG) + KNIFE ]