A billion is a number with two distinct definitions:
- 1,000,000,000, i.e. one thousand million, or 109 (ten to the ninth power), as defined on the short scale. This is now the meaning in both British and American English.
- 1,000,000,000,000, i.e. one million million, or 1012 (ten to the twelfth power), as defined on the long scale. This is one thousand times larger than the short scale billion, and equivalent to the short scale trillion. This is the historic definition of a billion in British English.
American English has always used the short scale definition in living memory but British English once employed both versions. Historically, the United Kingdom used the long scale billion but since 1974, official UK statistics have used the short scale. Since the 1950s, the short scale has been increasingly used in technical writing and journalism, although the long scale definition still enjoys some limited usage.
Another word for one thousand million is milliard, but this is used much less often in English than billion. Most other European languages — including Bulgarian, Croatian, Czech, Danish, Dutch, Finnish, French, Georgian, German, Hungarian, Italian, Norwegian, Polish, Portuguese, Romanian, Russian, Slovak, Spanish and Swedish — use milliard (or a related word) for the short scale billion, and billion (or a related word) for the long scale billion. Thus for these languages billion is thousand times larger than the modern English billion. However, in Russian, milliard (миллиард) is used for the short scale billion, and trillion (триллион) is used for the long scale billion.
According to the Oxford English Dictionary, the word billion was formed in the 16th century (from million and the prefix bi-, "two"), meaning the second power of a million (1,000,0002 = 1012). This long scale definition was similarly applied to trillion, quadrillion and so on. The words were originally French, and entered English around the end of the 17th century. Later, French arithmeticians changed the words' meanings, adopting the short scale definition whereby three zeros rather than six were added at each step, so a billion came to denote a thousand million (109), a trillion (1012), and so on. This new convention was adopted in the United States in the 19th century, but Britain retained the original long scale use. France, in turn, reverted to the long scale in 1948.
In Britain, however, under the influence of American usage, the short scale came to be increasingly used. In 1974, Prime Minister Harold Wilson confirmed that the government would use the word billion only in its short scale meaning (one thousand million). In a written answer to Robin Maxwell-Hyslop MP, who asked whether official usage would conform to the traditional British meaning of a million million, Wilson stated: "No. The word 'billion' is now used internationally to mean 1,000 million and it would be confusing if British Ministers were to use it in any other sense. I accept that it could still be interpreted in this country as 1 million million and I shall ask my colleagues to ensure that, if they do use it, there should be no ambiguity as to its meaning."
- "How many is a billion?". oxforddictionaries.com.
- Dent, Susie (28 October 2011). "How billions and trillions changed". BBC News. Retrieved 10 July 2015.
- Cracknell, Richard; Bolton, Paul (January 2009). Statistical literacy guide: What is a billion? And other units (PDF) (Report). House of Commons Library. Retrieved 10 July 2015.
- OED (1989) entry for "billion".