The term America, for the lands of the western hemisphere, is believed to have been coined in 1507 after Amerigo Vespucci, an Italian explorer and cartographer. The full name of the country was first used officially in the Declaration of Independence, which was the "unanimous Declaration of the thirteen united States of America" adopted by the "Representatives of the united States of America" on July 4, 1776. The current name was finalized on November 15, 1777, when the Second Continental Congress adopted the Articles of Confederation, the first of which states, "The Stile of this Confederacy shall be 'The United States of America.'" Common short forms and abbreviations of the United States of America include the United States, the U.S., the U.S.A., and America. Colloquial names for the country include the U.S. of A. and the States. Columbia, a once popular name for the Americas and the United States, was derived from Christopher Columbus. It appears in the name "District of Columbia". A female personification of Columbia appears on some official documents, including certain prints of U.S. currency.
The standard way to refer to a citizen of the United States is as an American. Though United States is the formal adjective, American and U.S. are the most common adjectives used to refer to the country ("American values," "U.S. forces"). American is rarely used in English to refer to people not connected to the United States.
The phrase "the United States" was originally treated as plural—e.g, "the United States are"—including in the Thirteenth Amendment to the Constitution, ratified in 1865. However, it became increasingly common to treat the name as singular—e.g., "the United States is"—after the end of the Civil War. The singular form is now standard, while the plural form is retained in the set idiom "these United States."