A wain's a type of horse-drawn, load-carrying vehicle, used for agricultural purposes rather than transporting people, for example a haywain. It normally has four wheels but the term has now acquired slightly poetical connotations so isn't always used with technical correctness. However, a two-wheeled 'haywain' would be a hay cart, as opposed to a carriage. "Wain"'s also an archaic term for chariot. Builders of wains were known as wainwrights, just as the builders of carts were known as cartwrig… (More on Wain)