jackknife

Meanings

1. 1
   noun

   a large pocketknife whose blade folds into the handle

   He cut the twine with a jackknife and folded the blade away.

2. 2
   noun

   a dive in which the body bends sharply at the waist before straightening

   The diver performed a clean jackknife from the high platform.

3. 3
   verb

   of an articulated vehicle, to fold sharply at the joint between its sections

   The truck jackknifed on the icy road and blocked both lanes.

A compound of jack + knife, originally naming a large folding pocketknife. The diving and vehicle senses arose from resemblance to the sharply folded blade and handle.

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