In the early days of the United States, the term "Dollar" was commonly known as a coin minted by Spain called the Spanish Milled Dollar.

In the early days of the United States, the term "Dollar" was commonly known as a coin minted by Spain called the Spanish Milled Dollar. These coins were the standard money then in use in the country. On April 2, 1792, Alexander Hamilton, then the Secretary of the Treasury, made a report to Congress having scientifically determined the amount of silver in the Spanish Milled Dollar coins that were then in current use by the people. As a result of this report, the Dollar was defined as a unit of measure of 371 4/16th grains of pure silver or 416 grains of standard silver (standard silver being defined as 1,485 parts fine silver to 179 parts alloy). Therefore paper is not the dollar, instead, it is 'worth', not 'is', 1 dollar (US Silver certificate.) In section 20 of the Act, it is specified that the "money of account" of the United States shall be expressed in those same "dollars" or parts thereof. All of the minor coins were also defined in terms of percentages of the primary coin — the dollar — such that a half dollar contained 1/2 as much silver as a dollar, quarter dollars contained 1/4 as much, and so on.

In an act passed on January 18, 1837, the alloy was changed to 10%, having the effect of containing the same amount of silver but being reduced in weight to 412 1/4 grains of standard silver which was changed to 90% pure and 10% alloy. On February 21, 1853 the amount of silver in the fractional coins was reduced so that it was no longer possible to combine the fractional coins to come up with the same amount of silver that was in the dollar.

Various acts have been passed over the years that affected the amount and type of metal in the coins minted by the United States such that today, there is no legal definition of the term "Dollar" to be found in any Statute of the United States.

Today, the closest definition to a dollar comes from the United States code Title 31, Section 5116, paragraph b, subsection 2, "The Secretary [of the Treasury] shall sell silver under conditions the Secretary considers appropriate for at least $1.292929292 a fine troy ounce." However Federal Reserve banks are only prejudiced to deliver tax credits instead of money. The silver content of US coinage was mostly removed in 1965 and the dollar essentially became a baseless free-floating fiat currency, though the US Mint continues to make silver $1 bullion coins at this weight.

Continued Chinese demand for silver led several countries, notably the United Kingdom, United States, and Japan, to mint trade dollars in the 19th and early 20th centuries, often of slightly different weights to their domestic coinage. Silver dollars reaching China (whether Spanish, Trade, or other) were often stamped with Chinese characters known as "chop marks", which indicated that that particular coin had been assayed by a well-known merchant and determined genuine.

The German name Thaler comes from the Bohemian coin minted in the 16th century from silver mined at Joachimsthal in Bohemia.

The German name Thaler comes from the Bohemian coin minted in the 16th century from silver mined at Joachimsthal in Bohemia. Not long after issuance, these coins gained the name Joachimsthalers. Subsequently, the coins were called "thaler" regardless of the issuing authority, and continued to be minted until 1872.

The name is historically related to the tolar in Germany, the Reichsthaler in Slovenia (Slovenian tolar) and Bohemia, the daalder in the Netherlands, and daler in Sweden, Denmark, and Norway. "Guildiner" can be traced to 1486 when Archduke Sigismund of Tyrol, a small state north of Venice, issued a dollar-sized coin which was referred to as a "guildiner". Silver supplies were small which limited coinage.

The Dutch lion dollar circulated throughout the Middle East and was imitated in several German and Italian cities. It was also popular in the Dutch East Indies as well as in the Dutch New Netherlands Colony (New York). The lion dollar also has circulated throughout the English colonies during the 17th and early 18th centuries . Examples circulating in the colonies were usually fairly well worn so that the design was not fully distinguishable, thus they were sometimes referred to as "dog dollars." This Dutch currency made its way to the east coast due to the increased trading by colonial ships with other nations. By the mid-1700s, it was replaced by the Spanish 8 reales.

The name "Spanish dollar" was used for a Spanish coin, the "real de a ocho" and later peso. It was worth eight reals (hence the nickname "pieces of eight"), and was widely circulated during the 18th century in the Spanish colonies in the New World, and in Spanish territories in Asia, namely in the Philippines. The use of the Spanish dollar and the Maria Theresa thaler as legal tender for the early United States and its fractions were the mainstay of commerce. They are the reasons for the name of the nation's currency.[citation needed] By the American Revolution in 1775, these Spanish coins became even more important. They backed paper money authorized by the individual colonies and the Continental Congress. 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; however this is not rare in Shakespeare's work.

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 US troops came to the UK during World War II. At the time a US dollar was worth about 5s., so some of the US soldiers started calling it a dollar. Consequently, they called the half crown "half a dollar". The expression caught on among some locals and could be heard into the 1960s.