(1):
(n.) A long, hollow vessel, generally for holding water or other liquid, especially one formed by excavating a log longitudinally on one side; a long tray; also, a wooden channel for conveying water, as to a mill wheel.
(2):
(n.) Any channel, receptacle, or depression, of a long and narrow shape; as, trough between two ridges, etc.
(3):
(n.) The transverse section of a cyclonic area where the barometric pressure, neither rising nor falling, has reached its lowest point.