jack-knife

Other spellings

• jackknife

Noun

Singular jack-knife

Plural jack-knives

Utility jack-knives.

A jack-knife dive.

A jack-knifed truck.

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

Verb

Plain form jack-knife

Third-person singular jack-knifes

Past tense jack-knifed

Past participle jack-knifed

Present participle jack-knifing

A truck (lorry) jack-knifing.

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