"penstock" in the noun sense
1. sluicegate, sluice valve, floodgate, penstock, head gate, water gate
regulator consisting of a valve or gate that controls the rate of water flow through a sluice
2. sluice, sluiceway, penstock
conduit that carries a rapid flow of water controlled by a sluicegate
Source: WordNet® (An amazing lexical database of English)
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