jack-knife

A man uses a jack-knife to cut a piece of rope.

Definition

1. Noun:

   • A type of folding knife: "jack-knife" refers to a large pocketknife with a blade that folds into the handle, typically spring-loaded.
   • A dive or acrobatic movement: In diving or gymnastics, a "jack-knife" is a position or movement where the body bends at the waist, forming an angle, often with the hands touching the feet or toes.
   • A vehicle accident: In trucking or transportation, a "jack-knife" occurs when a trailer swings out of alignment with the tractor, forming a sharp angle, often causing a crash.

2. Verb:

   • To fold or bend sharply: "jack-knife" means to bend or collapse in the middle, like a folding knife closing.
   • To cause a trailer to swing out of alignment: In driving, to "jack-knife" a vehicle means to lose control, causing the trailer to angle sharply relative to the tractor.

Usage Examples

• Noun:

  • He pulled out his jack-knife to cut the rope. (A folding pocketknife used for cutting.)
  • The diver executed a perfect jack-knife from the high board. (A dive where the body bends at the waist.)
  • The truck driver avoided a jack-knife on the icy road. (A dangerous trailer alignment accident.)

• Verb:

  • The metal rod jack-knifed under the pressure. (It bent sharply in the middle.)
  • The driver slammed on the brakes, causing the truck to jack-knife. (The trailer swung out of control.)

Advanced Usage

• "to jack-knife a dive": to perform a dive with a sharp bend at the waist.

  • She jack-knifed into the pool, making a small splash. (She dived with a precise, folded body position.)

• "a jack-knife turn": a very sharp, sudden change in direction.

  • The car made a jack-knife turn to avoid the obstacle. (An abrupt, angled turn.)

Variants and Related Words

• Jackknife (n/adj): The same word, often written without a hyphen.
  • He used a jackknife to open the package. (The same folding knife.)
• Jackknifing (n/adj): The action or process of bending sharply or causing a trailer to swing out.
  • The jackknifing of the truck blocked the highway. (The accident caused by the trailer swinging.)

Synonyms

• For the knife: , .
• For the dive: , .
• For the accident: , .

Phrasal Verbs

• Jack-knife off: to separate or detach by bending sharply.
  • The branch jack-knifed off the tree in the storm. (It broke off with a sharp bend.)

Related Idioms

• "fold like a jack-knife": to collapse or give way suddenly and completely.

  • The old chair folded like a jack-knife under his weight. (It collapsed sharply in the middle.)

• "pull a jack-knife": to perform a sudden, dramatic bend or turn.

  • The gymnast pulled a jack-knife on the bars. (She executed a sharp bending move.)