octillion

UK: /ɒkˈtɪljən/ US: (ok til′yən)

Inflections of 'octillion' (n):

octillions

npl (Used without a preceding number—e.g. "There must be octillions of bacteria on the planet.")

octillion

npl (Used with a preceding number—e.g. "The answer to the sum is 2 octillion.")

WordReference Random House Unabridged Dictionary of American English © 2025

oc•til•lion  (ok til′yən), n., pl. -lions, (as after a numeral) -lion, adj. 
n. 

1. a cardinal number represented in the U.S. by 1 followed by 27 zeros, and in Great Britain by 1 followed by 48 zeros.

adj. 

2. amounting to one octillion in number.

• French, equivalent. to oct- oct- + -illion, as in million
• 1680–90

oc•til′lionth, n., adj. 

Collins Concise English Dictionary © HarperCollins Publishers::

octillion / ɒkˈtɪljən/ noun

1. (in Britain and Germany) the number represented as one followed by 48 zeros (10⁴⁸)
2. (in the US, Canada, and France) the number represented as one followed by 27 zeros (10²⁷)

Etymology: 17th Century: from French, on the model of million

ocˈtillionth adjective , noun