/ Dictionary / Index E exo-: Meaning and Definition of Find definitions for: exo- Pronunciation: [key] a combining form meaning “outside,” “outer,” “external,” used in the formation of compound words: exocentric. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. ex nihilo nihil fit* exobiology Related Content Daily Word Quiz: soporific Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language