/ Dictionary / Index I ignis fatuus: Meaning and Definition of Find definitions for: ig•nis fat•u•us Pronunciation: (ig'nis fach'-us), [key] — pl. ig•nes fat•u•i a flitting phosphorescent light seen at night, chiefly over marshy ground, and believed to be due to spontaneous combustion of gas from decomposed organic matter. something deluding or misleading. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. ignimbrite ignite 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