(slang, derogatory) Jack in the Box (the chain of fast food restaurants).

(UK, slang, obsolete) An attendant at the watermen's stairs on the river and seaport towns.

(historical) A person who wore a pyramidal or conical wicker or wooden framework decorated with foliage, as part of May Day processions in England.

A compact folding knife. / The front-dive pike, in which the body folds and unfolds. / (colloquial) A semi-trailer truck accident in which the vehicle mimics the closing of a jack-knife.

To fold in the middle, as a jackknife does. / (colloquial) To cause a semi-trailer truck to fold like a jackknife in a traffic accident.

A physical exercise performed by jumping to a position with the legs spread wide and the hands touching overhead and then returning to a position with the feet together and the arms at the sides.

Alternative spelling of blackjack / Caranx lugubris, a gamefish / Bidens spp., from the family of Asteraceae / (obsolete) The larva of a turnip sawfly (Athalia rosae) / (mining, mineralogy) Sphalerite.

Alternative spelling of crackerjack

a public executioner / the gallows / death / the devil

Alternative spelling of hijack