[bil-yuh n]

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

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


equal in number to a billion.

Origin of billion

1680–90; < French, equivalent to b(i)- bi-1 + -illion, as in million
Related formsbil·lionth, adjective, noun Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for billionth

Contemporary Examples of billionth

  • The temperature of Cygnus X-1 from Hawking radiation is roughly a billionth of a degree above absolute zero.

    The Daily Beast logo
    Black Holes Exist. So Does Bad Science

    Matthew R. Francis

    September 28, 2014

  • We've moved from computers with a trillionth of the power of a human brain to computers with a billionth of the power.

    The Daily Beast logo
    The Robots Are Coming!

    Justin Green

    May 14, 2013

Historical Examples of billionth

British Dictionary definitions for billionth


noun plural -lions or -lion

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


(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
Derived Formsbillionth, adjective, noun

Word Origin for billion

C17: from French, from bi- 1 + -llion as in million
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for billionth

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1680s, from French billion (originally byllion in Chuquet's unpublished "Le Triparty en la Science des Nombres," 1484; copied by De la Roche, 1520), from bi- "two" (see bi-) + (m)illion.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.

Online Etymology Dictionary, © 2010 Douglas Harper