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]