/ Dictionary / Index U undecillion: Meaning and Definition of Find definitions for: un•de•cil•lion Pronunciation: (un"di-sil'yun), [key] — n., pl. adj. -lions, -lion, —n. a cardinal number represented in the U.S. by 1 followed by 36 zeros, and in Great Britain by 1 followed by 66 zeros. —adj. amounting to one undecillion in number. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. undecided undecylenic acid Related Content Daily Word Quiz: secular Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language