Jackknifed

Part of speech: verb

Definitions

1. To fold or bend abruptly, often describing a vehicle whose trailer has hinged sharply against the cab
2. To bend or collapse suddenly and sharply, particularly when referring to a vehicle's trailer folding against its towing part
3. To undergo a sudden, sharp bending motion, notably used for vehicles whose trailers fold in a hinged manner against the truck

Etymology: Jackknife began as a tool and only later became a verb of motion. The knife was a large, sturdy folding pocketknife, and "jack" was a common word for a handy, general-purpose object, as in "jack-of-all-trades." The folding blade that snaps shut against its handle gave the name to a range of other things that fold on a single hinge, such as the jackknife dive, in which a diver bends sharply at the waist and then straightens. The verb follows the same picture. A tractor-trailer that skids or brakes hard can swing its trailer around until it folds against the cab, forming a sharp V shape much like an open pocketknife closing on its hinge. That sudden, hinged bend is what "jackknifed" describes. The past tense form is simply the regular verb "jackknife" with its -ed ending, used for a vehicle that has already folded this way.

Synonyms: folded, bent, collapsed, curved, pivoted