/ Dictionary / Index O omicron: Meaning and Definition of Find definitions for: om•i•cron Pronunciation: (om'i-kron", ō'mi-), [key] — n. the 15th letter of the Greek alphabet (O, o). the vowel sound represented by this letter. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: omicron (Thesaurus) Omi ominous Related Content Daily Word Quiz: spectral Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language