bracketyoudaoicibaDictYouDict[bracket 词源字典]
bracket: [16] The word bracket appears to have come from medieval French braguette, which meant ‘codpiece’, a resemblance evidently having been perceived between the codpiece of a pair of men’s breeches and the ‘projecting architectural support’ which was the original meaning of bracket in English. Before the word even arrived in English, it had quite an eventful career.

The French word was a diminutive form of brague, which in the plural meant ‘breeches’. It was borrowed from Old Provençal braga, which got it from Latin brāca; Latin in turn acquired it from Gaulish brāca, but the Gaulish word seems ultimately to have been of Germanic origin, and to be related to English breeches.
=> breeches[bracket etymology, bracket origin, 英语词源]
bracket (n.)youdaoicibaDictYouDict
1570s, bragget, "architectural support," probably from Middle French braguette "codpiece armor" (16c.), from a fancied resemblance of architectural supports to that article of attire (Spanish cognate bragueta meant both "codpiece" and "bracket"), diminutive of brague "knee pants," ultimately from Gaulish *braca "pants," itself perhaps from Germanic (compare Old English broc "garment for the legs and trunk;" see breeches). The architectural meaning also might reflect the "breeches" sense, on the notion of two limbs or of appliances used in pairs. The typographical bracket is first recorded 1750, so called for its resemblance to double supports in carpentry (a sense attested from 1610s). Senses affected by Latin brachium "arm."
bracket (v.)youdaoicibaDictYouDict
1797, of printed matter, "to enclose in brackets," from bracket (n.). Also, "to couple or connect with a brace" (1827), also figurative, "to couple one thing with another" in writing (1807). Artillery rangefinding sense is from 1903, from the noun (1891) in the specialized sense "distance between the ranges of two shells, one under and one over the object." Related: Bracketed; bracketing. In home-building and joinery, bracketed is attested by 1801.