'Penstock' definitions:

Definition of 'penstock'

noun

Regulator consisting of a valve or gate that controls the rate of water flow through a sluice [syn: sluicegate, sluice valve, floodgate, penstock, head gate, water gate]

noun

Conduit that carries a rapid flow of water controlled by a sluicegate [syn: sluice, sluiceway, penstock]

From: GCIDE

Penstock \Pen"stock\, n. [Etymol. uncertain; perh. fr. pen an inclosure + stock.]
1. A close conduit or pipe for conducting water, as, to a water wheel, or for emptying a pond, or for domestic uses. [1913 Webster]
2. The barrel of a wooden pump. [1913 Webster]