originally, a silver coin that circulated in many European countries; in modern times, the name of the standard monetary unit in the United States, Canada, Australia, New Zealand, and other countries. The Spanish peso, or piece of eight, which circulated in the Spanish and English colonies in America, was known as a dollar by the English-speaking peoples. Familiarity with this coin resulted in the official designation of the United States monetary unit as the dollar in 1792. Canada adopted the dollar and monetary decimal system in 1858; Australia in 1966; and New Zealand in 1967.

The word itself is a modified form of the Germanic word thaler, a shortened form of Joachimst(h)aler, the name of a silver coin first struck in 1519 under the direction of the count of Schlick, who had appropriated a rich silver mine discovered in St. Joachimsthal (Joachim's dale), Bohemia. These coins were current in Germany from the 16th century onward, with the various spelling modifications such as daler, dalar, daalder, and tallero. Only in 1873 was the thaler replaced by the mark as the German monetary unit.

In the United States, paper money has been issued in dollar amounts since 1861. Portraits of American political figures appear on the various denominations of U.S. banknotes: