It was considered dÃ©classÃ© to refer to one's own townhouses, estates or villas (or those of friends) as mansions and modern etiquette books still advise that the terms house, big house or great house be used instead.
Waste weir. A waste weir on a navigable canal is a slatted gate on each canal level or pound, to remove excess water and to drain the canal for repairs or for the winter shutdown.
Weirs are small dams used to control water flow in rivers. They don't actually bottle up the water like big dams, but the river will form a pool behind the weir. The water will flow continuously over the weir, dropping (usually) 4-6 feet to the river level below.