What does decillion mean?
A decillion is a cardinal number representing ten raised to the thirty-third power — a one followed by thirty-three zeros — under the short-scale convention now standard throughout the English-speaking world. Like other members of the -illion family, it was formed by combining the Latin numeral for its tier with the familiar ending of million, so its name signals 'tenth' among the great named powers of a thousand. In everyday use the word is rare and formal, surfacing mainly in mathematics, physics, and astronomy when writers want a vivid name for an almost incomprehensibly large quantity, such as counts of atoms or astronomical odds. Historically, British usage followed the long scale, under which a decillion meant 10⁶⁰; this discrepancy is why precise texts prefer scientific notation. Knowing the word equips readers to grasp the staggering scale of numbers that exceed any practical enumeration.
nounThe number ten raised to the thirty-third power (10³³), written as a one followed by thirty-three zeros. In the older British long-scale system, it denoted ten to the sixtieth power (10⁶⁰).
- The cardinal number equal to 10³³ (a 1 followed by 33 zeros), as defined in the American short scale now standard in English-speaking countries.
- (Historical, British long scale) The cardinal number equal to 10⁶⁰.
"Estimates of the number of atoms in a large galaxy can approach a decillion."
"The odds of such an event occurring by chance are roughly one in a decillion."
"Older British textbooks used the long scale, under which a decillion meant 10⁶⁰ rather than 10³³."
Pluralizes normally when referring to multiple instances of the number or indefinite large amounts.
"There are decillions of possible arrangements."
If you counted one number per second since the Big Bang, you wouldn't even be close to a decillion — not by a factor of billions upon billions.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of decillion
Decillion entered English in the early 19th century, formed from Latin decem ('ten') combined with the -illion suffix patterned on million, following Chuquet's system for naming successive powers of a thousand. It belongs to the same Latin root family as decimal, decade, and December, all tracing back to decem. Its numerical value shifted between the traditional British long scale (10⁶⁰) and the American short scale (10³³), with the short scale now prevailing internationally.
How decillion is actually used
Formal or technical register; decillion appears chiefly in mathematics, astronomy, and discussions of very large quantities. Because the -illion names differ between the short scale used in the US and modern Britain and the historical long scale used in much of Europe, careful writers often clarify with scientific notation (10³³).
Easily confused with decillion
A zillion is an indefinite, informal term for an enormous but unspecified number, whereas a decillion is a precisely defined power of ten.
A nonillion is 10³⁰, three orders of magnitude smaller than a decillion, which is 10³³.