noun, plural bil·lions, (as after a numeral) bil·lion.

  1. a cardinal number represented in the U.S. by 1 followed by 9 zeros, and in Great Britain by 1 followed by 12 zeros.
  2. a very large number: I’ve told you so billions of times.


  1. equal in number to a billion.

noun plural -lions or -lion

  1. one thousand million: it is written as 1 000 000 000 or 10 9
  2. (formerly, in Britain) one million million: it is written as 1 000 000 000 000 or 10 12
  3. (often plural) any exceptionally large number


  1. (preceded by a or a cardinal number)
    1. amounting to a billionit seems like a billion years ago
    2. (as pronoun)we have a billion here

1778, from billion + -th (2).


1680s, from French billion (originally byllion in Chuquet’s unpublished “Le Triparty en la Science des Nombres,” 1484; copied by De la Roche, 1520), from bi- “two” (see bi-) + (m)illion. A million million in Britain and Germany (numeration by groups of sixes), which was the original sense; subsequently altered in French to “a thousand million” (numeration by groups of threes) and picked up in that form in U.S., “due in part to French influence after the Revolutionary War” [David E. Smith, “History of Mathematics,” 1925]. France then reverted to the original meaning in 1948. British usage is truer to the etymology, but U.S. sense is said to be increasingly common there in technical writing.

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