bræs

Old English bræs appeared before the year 1000, meaning the copper-zinc alloy we still call brass. Its origin is a mystery. It has no convincing cognates in other Germanic languages — Old Norse, Old High German, and Gothic have nothing like it. Some linguists have suggested a connection to Old French brasser (to brew or mix), which might reference the alloying process. Others think it is pre-Germanic, a substrate word from whatever language the Anglo-Saxons displaced.

Brass was important in the ancient world but always secondary to bronze. The Babylonians made brass objects by 3000 BCE, though they probably did not distinguish it from bronze. The Romans called it orichalcum and aurichalcum — 'gold-copper' — because the zinc content gave it a golden color. English kept the word bræs where Latin used a compound, which says something about how each culture related to the metal.

The idioms piled up. 'Brass tacks' appeared by the 1860s in American English, meaning the real substance of a matter — possibly from the brass tacks used to measure fabric in dry-goods stores. 'Top brass' emerged from military slang around 1900, referring to officers whose insignia were made of brass. 'Brass neck' meant shameless audacity in British slang, from the idea of a neck so hard it could not blush.

The musical sense — brass instruments — dates from the 1500s, when trumpets, trombones, and horns were literally made of brass. A brass section, a brass band, a brass player. The word named both the raw material and the sound it produced, which is unusual for a metal. Nobody calls a guitar a 'wood instrument.' But brass became a category of music because the alloy was inseparable from the tone.