What does octillionth mean?
Octillionth is the ordinal form of octillion. In the short-scale numbering system used in modern English, an octillion is 10^27, or one followed by 27 zeros, so the octillionth item in an ordered series is the item in position 10^27. The term can also describe one of 10^27 equal parts of a whole, as in a quantity being only an octillionth of the original. As a noun, octillionth denotes the ordinal number itself or something occupying that position. The word belongs primarily to mathematical and highly formal English and is encountered far less often than billionth or trillionth. Because the names of very large numbers vary between the short and long scales, especially for words such as billion, trillion and octillion, a reader may need additional context to determine the intended value.
Denoting the ordinal position 10^27 in a sequence, or one of 10^27 equal parts of a whole.
"The remaining fraction was an octillionth of the initial quantity."
Rare and chiefly mathematical; the numerical value assumes the short scale unless otherwise stated.
The ordinal number corresponding to position 10^27, or an item occupying that position.
"Reaching the octillionth would require an unimaginable number of steps."
More common in mathematical and formal writing than in everyday speech.
An octillionth divides a whole into 10^27 equal parts—a scale reached only by moving the decimal point 27 places.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does octillionth come from?
The word combines octillion, formed from Latin octo, meaning “eight,” with the Latin-derived million, from mille, meaning “thousand,” with the native English ordinal suffix -th. Its relatives octet, octave and octavo also trace to Latin octo, though they developed through separate English borrowings and formations. The modern sense follows the use of octillion for 10^27 in the short scale.
Related word forms
How octillionth is actually used
This is a rare, mathematically inflected form used mainly in formal or technical contexts. In modern English it normally assumes the short scale, but older long-scale conventions assign a different value to the word octillion; context or an explicit power of ten may therefore be necessary.
Easily confused with octillionth
An octillion is the number 10^27 in the short scale, whereas an octillionth is the corresponding ordinal position or one of 10^27 equal parts.