Longman Dictionary of Contemporary English
Douglas Harper's Etymology Dictionary
Wiktionary
n. A vertical pipe or conduit that carries rainwater from the scupper, guttering of a building to a lower roof level, drain, ground or storm water runoff system.
Wikipedia
A downspout, waterspout, downpipe, drain spout, roof drain pipe, leader, or rone ( Scotland) is a pipe for carrying rainwater from a rain gutter.
Downspouts are usually vertical and usually extend down to ground level. The water is directed away from the building's foundation, to protect the foundations from water damage. The water is usually piped to a sewer, or let into the ground through seepage.
The first ever downspout to be installed was in 1240 on the Tower of London, as it was whitewashed and the newly painted walls had to be protected from the rain. Decorative heads are sometimes added, these being low-height gargoyles.
Usage examples of "downspout".
The rain hit the windows in taps and spatters, small and countable, and then it was everywhere, banging the roof of the sunporch and filling the downspouts, and they sat and listened to it.
One twelve-bedroom Tudor castle, I glued the downspouts on the wrong gable ends and melted everything by trying to fix it with a chemical solvent.
Water foamed out of downspouts into nearby drains, drizzled off roofs, puddled in the streets, and overflowed gutters, and because the city was almost entirely dark, the pools and streams looked more like oil than water.
Shortly before the gutters and downspouts were hung, an obscene drawing accompanied by a one-syllable Anglo-Saxon word was scrawled on the fanhghted front door in soft yellow chalk.
The pools, slightly raised above the level of the street and about two meters across and a meter deep, ranged from five to ten meters in length and collected water from the larger buildings' downspouts.
A smile edged over me as I spotted Jenks sitting on the curve of a downspout, tapping it with his boot heels.