/ Dictionary / Index U UFO: Meaning and Definition of Find definitions for: UFO Pronunciation: (y'ef'ō' or, sometimes, y'fō), [key] — pl. UFO's, UFOs. any unexplained moving object observed in the sky, esp. one assumed by some observers to be of extraterrestrial origin. Also calledCf. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: ufo (Thesaurus) U.F.C. ufology Related Content Daily Word Quiz: rustic Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language