Hydropower

The seventeenth entry is o canal de restituição, and the English for it is a word a reader can meet a hundred times without ever once looking at it: « the tailrace ». A « race », in this sense, is a channel of moving water, and the word is very old. It came into English from Old Norse rás, a running or a rush, and a rush of water was among the first things it named. Every mill on every stream then had two of them: « the headrace » brought the water to the wheel and « the tailrace » carried it away again, while « the millrace » could be either. All three have survived into the language of dams, where the tailrace is the channel that hands the water back to the river below the turbine. Two things follow. The contest that is also called « a race » is the same old word, a running of another kind, so nothing here is borrowed from sport. And the compounds are written solid, « tailrace » and « headrace », while the bare noun keeps its article: the water leaves by the race.