/ Dictionary / Index S septillion: Meaning and Definition of Find definitions for: sep•til•lion Pronunciation: (sep-til'yun), [key] — n., pl. adj. -lions, -lion, —n. a cardinal number represented in the U.S. by 1 followed by 24 zeros, and in Great Britain by 1 followed by 42 zeros. —adj. amounting to one septillion in number. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: septillion (Thesaurus) Sept-Îles septimal Related Content Daily Word Quiz: deleterious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language