a river of the United States of North America, formed by the confluence of the north and south branches, both of which take their rise in the Alleghanies, and unite on the northern frontier of Virginia. Through the whole of its course it separates that state from Maryland and the district of Columbia, flowing E. and S.E., till it falls into Chesapeake Bay. Its length from the junction of the two branches is about 350 miles; and its breadth at its mouth 6 or 8 miles. Its largest affluent is the Shenandoah, which has a volume of water little inferior to the main river. It is navigable for ships of the line to Washington, the capital of the United States, 120 miles above its mouth; but above this its course is interrupted by numerous falls and rapids.