A pipe that carries water away from a building or roof to a drainage system or sewers.
Compound of drain + pipe, combining in English during the Industrial Revolution as plumbing systems became standard in buildings (1800s).
Drainpipe trousers were named after these pipes because they're so narrow—1950s teddy boys wore them and they caused actual controversy because parents thought the style was too rebellious. Clothing gets named after random objects.
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