The Potomac is a river in the eastern United States. It runs past Washington, D.C., and in that stretch it is the line between Maryland (and the capital) on one side and Virginia on the other; farther west it also touches West Virginia. Americans say it in news, history, and weather — floods, cherry trees, politics — because the capital sits on its banks. You stress the middle: puh-TOH-muk. It is a place name, so it takes a capital P; people say the Potomac, like the Thames. Though actually the tidy map-line (“this state from that state”) is simpler than the whole river: it is long, it has falls, and the name itself was written many ways before it settled. Scholars do not agree on one English meaning of the old Algonquian name; you will hear “river of swans,” “place where people trade,” or “place to which tribute is brought.” Native people called the river above the falls Cohongorooton, “river of geese,” and early visitors found both geese and swans there. European spellings moved from Patawomeke to Patowmack in the 1700s and later to Potomac. The US Board on Geographic Names made Potomac the official spelling in 1931.