Jury-rig: To assemble for temporary service; to improvise.
Jury-rig was originally a nautical term meaning "to improvise the rigging on a ship." A related term, jury-mast, refers to a temporary mast that replaces one that has been broken or blown away; its first recorded appearance in print was in Captain John Smith's A Description of New England (1616). In both cases, the jury has nothing to do with a jury of one's peers or with the legal system generally; although its origin is uncertain, it most likely comes from a different Latin root, adjutare ("to aid"), via Old French ajurie.
Jury-rig is sometimes seen, erroneously, as jerry-rig, by association with jerry-built, a much more recent word. (The Oxford English Dictionary says it first appeared in print in 1869.) Jerry-built means "built of substandard or insufficient materials"—that is, shoddy.1 The jerry- in jerry-built is believed to come from the male nickname Jerry, possibly by association with some long-forgotten Jerry the Bad Builder.
During World War I Jerry acquired a new meaning: it was one of many nicknames for a German soldier (and it was sometimes spelled Gerry). The containers German soldiers used for carrying water or gasoline came to be called jerry cans by their British adversaries.
Jerry has a long list of additional meanings, including a machine for shearing cloth, a noise made by printers, an abbreviation for jerry-shop (from Tom-and-Jerry shop, "a low ale-house," according to the OED), and (chiefly in Australia and New Zealand), "to understand or realize."
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1 Shoddy, like the jerry in jerry can, has a wartime provenance, at least in its current sense. It was originally a noun meaning "wool adulterated with cheap fibers"; it became an adjective during the U.S. Civil War, when war profiteers were labeled "shoddy millionaires."