1 a four-wheeled vehicle for heavy loads, often with a removable tilt or cover.
2 Brit. a railway vehicle for goods, esp. an open truck.
3 a trolley for conveying tea etc.
4 (in full water-wagon) a vehicle for carrying water.
5 US a light horse-drawn vehicle.
6 colloq. a motor car, esp. an estate car.
Phrases and idioms:
on the wagon (or water-wagon) sl. teetotal. wagon-roof (or -vault) = barrel vault.
Etymology: earlier wagon, wag(h)en, f. Du. wag(h)en, rel. to OE waeliggn WAIN
Useful english dictionary. 2012.