A brig, in ordinary English, is a two-masted sailing ship with square sails on both masts. In American naval speech it is also the lock-up on a warship, and by extension a military jail or guardhouse. The two senses look unrelated until the ship-name is followed into the eighteenth century and then, in United States usage, from hull to cell.
A clipped ship name
The origin of the word brig is not an independent borrowing. It is a colloquial shortening of brigantine, already current in English by the early sixteenth century. Dictionaries do not agree on the first printed date for the short form. One standard American record puts it at 1712; other datings cluster around 1705–15; an early Oxford citation is from the London Gazette of 1720. All of them place the clipping in the first decades of the eighteenth century.
Brigantine itself entered English around the 1520s from French brigandin, later brigantin, and that French word from Italian brigantino. The Italian form is built on brigante — a skirmisher, irregular soldier, or pirate — plus the diminutive suffix -ino. On that reading a brigantino was a small fighting or raiding craft, not yet the later square-rigger. Brigante belongs with the verb brigare, to fight or brawl, and the noun briga, strife. From the same Italian cluster English later took brigand, brigade, and brigadier.
The still older source of Italian briga is unsettled. Some accounts point to a Celtic word for strength or power, comparing Welsh bri and Gaelic brigh, and then to a Proto-Indo-European root meaning heavy. Others leave the Italian noun without a firm ancestor. That last step is a hypothesis, not a settled chain, and it does not affect the English clipping.
How the short word split from its parent
At first brig was simply sailors’ shorthand for the same vessel as brigantine. The two names then drifted apart as rigs specialized. A brig came to mean a two-master square-rigged on both the foremast and the mainmast, usually with an extra fore-and-aft sail, the spanker or boom mainsail, on the main. Brigantine was kept for a mixed rig: square sails forward and a schooner-like fore-and-aft mainmast. A mixed-rig two-master was also called a hermaphrodite brig. In the eighteenth century the short word could still be used more loosely for ships of several sorts; the tighter technical sense is what survives in nautical English.
That rig made a handy small warship and a busy coastal trader. Naval brigs typically carried something like ten to eighteen guns on one deck and served as couriers, scouts, and training ships. Merchant brigs worked collier routes, coastal cargo, and sometimes ocean passages, including whaling and sealing. The same square sails that gave driving power down the trade winds also needed a large crew. By the later nineteenth century owners preferred schooners, barks, and steam, which could be worked with fewer hands. The type did not vanish: some vessels survive as sail-training ships, and the word remains the name of the rig.
Related names traveled with the English clipping. French took brick from English brig for the square-rigged two-master, while keeping brigantin for the older mixed type. German Brigg, Dutch brik, Swedish brigg, and Russian brig sit on the same path. They are sister forms of the ship-word, not of the Scottish homonym discussed below.
From hull to lock-up
The jail sense is American and later. One dictionary dates a place of confinement for offenders — first on a ship — to 1832. Other authorities put the ship’s jail a little later: American English by 1841, with an Oxford citation from 1852. The usual explanation is that worn-out brigs, taken out of fighting or trading service, were used as prison hulks, so the ship-type name stuck to the place where men were locked up. That account is widely repeated and only probable. An early twentieth-century American dictionary still marked the naval prison sense as of unknown origin, and at least one modern etymological handbook calls it obscure. What is not in doubt is the later spread: from a compartment on a man-of-war to a naval or Marine guardhouse, then, in slang, to a military prison more generally, and even, in tramp slang, to a police station. A verb, to brig, meaning to confine someone in that lock-up, is recorded in United States military slang in the twentieth century.
A different brig on the map
English also has brig in Scots and northern dialects as the ordinary word for a bridge. That form comes from Scots brig, from Old Norse bryggja, and is a doublet of standard English bridge, from Old English brycg. It has nothing to do with Italian fighting boats. A horse can be sent over the keystone of a brig in a Burns poem without launching a square-rigger. The two words simply collided in spelling.
The durable fact about the nautical brig is how little of the original Italian fight remains in the English syllable. A sixteenth-century raiding boat, cut down by sailors to three letters, first named a specific rig and then, in American naval English, a cell. The French borrowing brick is a useful reminder of that first cut: once English had shortened brigantine, other languages borrowed the stump.