The motor vehicle referred to as a sedan is so called because it has a front and rear seat. It borrows its name from a much different vehicle of a much different era: the sedan chair, a portable chair that is designed to carry one person and that is carried on poles by two people.
The origin of sedan is not known, but sedan chairs were used in London, Edinburgh, and other British cities in the 17th and 18th centuries. Although commonly associated with the wealthy, they could also be hired out for a fare, like taxis.