The dollar (represented by the dollar sign: "$") is the name of the official currency in several countries, dependencies and other regions. The United States dollar is the world's most widely circulated currency.

The name Thaler (from thal, or nowadays usually tal, "valley") came from the German coin Guldengroschen ("great guilder", being of silver but equal in value to a gold guilder), minted from the silver from a rich mine at Joachimsthal - Jáchymov (St. Joachim's Valley) in Bohemia (then part of the Holy Roman Empire, now part of the Czech Republic).

The name is related to the tolar in Slovenia (and historically in Bohemia), the daalder in the Netherlands and daler in Sweden, Denmark, and Norway. Of these, only the Slovenian Tolar is still in use; on 1 January 2007, however, it will be replaced by the euro.

The name "Spanish dollar" was used for a Spanish coin, the peso, worth eight reals (hence the nickname "pieces of eight"), which was widely circulated during the 18th century in the Spanish colonies in the New World. The use of the Spanish dollar and the Maria Theresa thaler as legal tender for the early United States are the reasons for the name of the nation's currency. However, the word dollar was in use in the English language as slang or mis-pronunciation for the thaler for about 200 years before the American Revolution, with many quotes in the plays of Shakespeare referring to dollars as money. Spanish dollars were in circulation in the Thirteen Colonies that became the United States, and were legal tender in Virginia.

Coins known as dollars were also in use in Scotland during the 17th century, and there is a claim that the use of the English word, and perhaps even the use of the coin, began at the University of St Andrews. This explains the sum of 'Ten thousand dollars' mentioned in Macbeth (Act I, Scene II), although the real Macbeth upon whom the play was based lived in the 11th century, making the reference anachronistic.

In the early 19th century, a British five-shilling piece, or crown, was sometimes called a dollar, probably because its appearance was similar to the Spanish dollar. This expression appeared again in the 1940s, when U.S. troops came to the UK during World War II. At the time a U.S. dollar was worth about 5s., so some of the U.S. soldiers started calling it a dollar. Consequently, they called the half crown "half a dollar", and the expression caught on among some locals and could be heard into the 1960s.

In the early days of the United States, the dollar was a defined unit of trade equal to 412.5 grains of 90% silver. Today there is no definition of any weight or measure associated with its exchange. The silver content of U.S. coinage was mostly removed in 1965 and the dollar essentially became a baseless free-floating fiat currency.

• The word buck—possibly an abbreviation from buckskin, an intrinsic "currency" for trade with American Indians known since 1746—has been recorded since 1856 and is widely used as a synonym for the dollars of many countries, including Australia, Canada, New Zealand and the United States. The latter term, skin, is also used as a synonym as is the possibly related term squaw money.
• Greenback, a nickname originally applied to a 19th-century United States Demand Note, is now a common specific reference to the U.S. dollar; it is not used for coins or dollars of other countries.

• The tala is based on the Samoan pronunciation of the word "dollar". Likewise, the name of the smaller unit, seneiti, equates to "cent".
• The Slovenian tolar has the same origin as dollar, i.e. thaler.

Some of these are called dollars in English, but by a different name in the native language of the country:

• Australian dollar (Australia)
• Barbadian dollar (Barbados)
• Bahamian dollar (Bahamas)
• Belizean dollar (Belize)
• Bermudian dollar (Bermuda)
• Bruneian dollar Brunei
• Canadian dollar Canada
• Caymanian dollar (Cayman Islands)
• East Caribbean dollar Organisation of Eastern Caribbean States
• Fijian dollar (Fiji)
• Guyanese dollar (Guyana)
• Hong Kong dollar
• Jamaican dollar (Jamica)
• Liberian dollar (Liberia)
• Namibian dollar (Namibia)
• New Zealand dollar
• Singapore dollar
• Solomon Islander dollar (Solomon Islands)
• Surinamese dollar (Suriname)
• New Taiwan dollar
• Trinidad and Tobago dollar
• United States dollar
• Zimbabwean dollar (see also Rhodesian dollar)

The name has also been applied to the international dollar, a hypothetical unit of currency that has the same purchasing power that the U.S. dollar has in the United States at a given point in time.

• Dollar sign
• U.S. one dollar bill
• List of circulating currencies

• Etymonline (word history) for "buck" and Etymonline (word history) for "dollar"
• Thesaurus (synonyms)
• The Source: Slang Dictionary

• Relative values of the US dollar, from 1790 to 2005