English

Noun

jack-knife, also jackknife, plural jack-knives or jackknives Note: the two spellings appear roughly equally common.

1. A compact folding knife

   He kept a jack-knife in his pocket for various tasks.

2. The front-dive pike , in which the body folds and unfolds.

   It took me hundreds of dives to master even the simple jackknife

3. (colloquial) A semi-trailer truck accident in which the vehicle mimics the closing of a jack-knife.

   I have seen several jack-knives along that dangerous stretch of road.

4. ( A statistical tool for error estimation, so called for its usefulness.

   The jackknife provides a reasonably robust way to measure error propagation.

Translations

• Dutch: zakmes n (1)
• Frisian: bûsmês n (1), knyft n (1)

Verb

jack-knife, past and past participle jack-knifed

1. To fold in the middle, as a jackknife does.

   The cat jackknifed in the air and landed gracefully on its feet.

2. (colloquial) To cause a semi-trailer truck to fold like a jackknife.

   Before I knew what was happening, I'd jack-knifed the rig like nobody's business.

   Before I knew what was happening, I'd jack-knifed like nobody's business.