The American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
- The ordinal number that matches the number octillion in a series.
- One of an octillion equal parts.
- oc·tilˈlionth adverb & adj.