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decillion

/dɪˈsɪljən/

A number equal to one followed by thirty zeros

From Latin dec (ten) + French mathematical formation illion (suffix for names of very large numbers).

noun
dec
Latin
decem
“ten,” the source of the numerical prefix
Modern English mathematical formation
dec-
Combining form meaning “ten” in names of large numbers
illion
French mathematical coinage
-illion
Suffix used in names of successive large-number units, modeled on million
Modern English
-illion
Numerical suffix forming names such as billion, trillion, and decillion
Combined
decillion
The prefix dec- combines with -illion to form the name of a very large number.
English
decillion
In the short-scale system, 10³⁰: one followed by thirty zeros; first attested in English in 1709
Modern English
decillion

A decillion is the sort of number that makes a bank vault look like a child’s piggy bank: in the modern short-scale system, it is 1 followed by 30 zeros. Its first half is a straightforward numerical survivor, the Latin decem, “ten,” which also gives us decade, decimal, and even December—originally the tenth month of the Roman year. The second half, -illion, belongs to a family of grand mathematical labels built around million and expanded through French and English usage. The word was already in print in 1709, in George Vaux’s translation of Johann Sturm’s Mathesis juvenilis, when mathematicians were still giving names to quantities that no one could realistically write out in ordinary prose. And there is a small trap here: “decillion” is not universally the same number in every naming system; under the long scale, historical European usage could assign it a much larger value. Remember it as “ten plus the -illion parade”—a Latin counting word boarding a French-made train of increasingly enormous numbers.

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