- 2the capital of the US; population 591,833 (est. 2008). It is coextensive with the District of Columbia, a federal district on the Potomac River with boundaries on the states of Virginia and Maryland. Founded in 1790, during the presidency of George Washington, it was planned and built as a capital city. Full name Washington DC.
Pronunciation: /ˌwɒʃɪŋˈtəʊnɪən/noun & adjective