[ kwo-dril-yuh n ]
/ kwɒˈdrɪl yən /

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

a cardinal number represented in the U.S. by 1 followed by 15 zeros, and in Great Britain by 1 followed by 24 zeros.


amounting to one quadrillion in number.

Origin of quadrillion

1665–75; quadr- + -illion (as in million)
Related formsquad·ril·lionth, noun, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for quadrillionth

  • But as this gives something like one thousand quadrillionth part of the density of water, we refuse to accept or even think of it.

British Dictionary definitions for quadrillionth


/ (kwɒˈdrɪljən) /


(in Britain) the number represented as one followed by 24 zeros (10 24)US and Canadian word: septillion
(in the US and Canada) the number represented as one followed by 15 zeros (10 15)


  1. amounting to this numbera quadrillion atoms
  2. (as pronoun)a quadrillion
Derived Formsquadrillionth, adjective

Word Origin for quadrillion

C17: from French quadrillon, from quadri- + -illion, on the model of 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 quadrillionth



1670s, from French quadrillion (16c.) from quadri- "four" (see quadri-) + (m)illion. Cf. billion. In Great Britain, the fourth power of a million (1 followed by 24 zeroes); in the U.S., the fifth power of a thousand (1 followed by 15 zeroes).

Online Etymology Dictionary, © 2010 Douglas Harper