(n.) A penstock.

Ferris wheel avenue bank bevel bezel blowhole brolly carousel cascade cataract channel chimney chute-the-chutes chutes collapse comedown country rock crash debacle debouch declension declination defluxion deposit descending descension descent dike door down downbend downcome downcurve downfall downflow downgrade downpour downrush downtrend downturn downward trend drogue chute drop dropping easy slope eaves trough egress emunctory escape estuary exhaust exit fall falling falls fleam floodgate flume flying horses force gangue gentle slope glacis grade gradient gravitation guide gutter hanging gardens harness helicline hillside inclination incline inclined plane launching ramp lode lodestuff loophole matrix merry-go-round mineral deposit opening ore bed out outcome outfall outgate outgo outlet pack parachute parachute jump pay dirt penstock pentrough pitch plummeting pore port pounce ramp rapid rapids riff riffle ripple roller coaster roundabout runway sally port sault scarp seesaw shaft shelving beach shoot shroud lines side sky dive slide slope sluice spiracle spout steep slope stiff climb stock stoop swing swoop talus tap teeter-totter trough umbrella vein vent ventage venthole vomitory waterfall way out weir whip whirligig