jackknife

Other spellings

• jack-knife

Noun

Singular jackknife

Plural jackknives

Utility jackknives.

A jackknife dive.

A jackknifed truck.

1. (countable) A jackknife is a compact folding knife.
2. (countable) (diving) A jackknife is a front-dive pike where the body folds and unfolds.
3. (countable) (informal) A jackknife is a semi-trailer truck accident where the vehicle mimics the closing of a jackknife.

Verb

Plain form jackknife

Third-person singular jackknifes

Past tense jackknifed

Past participle jackknifed

Present participle jackknifing

A truck (lorry) jackknifing.

1. (intransitive) If something jackknifes, it folds in the middle like a jackknife.
2. (intransitive) (informal) If a semi-trailer truck jackknifes, it folds like a jackknife in a traffic accident.