(informal, archaic) A person whose assistance is sought only in an emergency.

(mildly vulgar, slang) Nothing.

A device for inserting a loop in a main electric line-circuit, a plug being forced between two spring contacts.

plural of spring jack

A municipality of St. Louis County, Missouri, United States.

plural of mangrove jack

(Australia, obsolete) The mangrove heron, Butorides striatus. / (Australia) An edible marine and estuarine fish, Lutjanus argentimaculatus, of northern Queensland.

plural of jack screw

Alternative form of jackscrew

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