ignis fatuus

[ ig-nis fach-oo-uh s ]
/ ˈɪg nɪs ˈfætʃ u əs /

noun, plural ig·nes fat·u·i [ig-neez fach-oo-ahy] /ˈɪg niz ˈfætʃ uˌaɪ/.

Also called friar's lantern, will-o'-the-wisp. 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.

Origin of ignis fatuus

1555–65; < Medieval Latin: literally, foolish fire
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

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British Dictionary definitions for ignis fatuus

ignis fatuus

/ (ˈɪɡnɪs ˈfætjʊəs) /

noun plural ignes fatui (ˈɪɡniːz ˈfætjʊˌaɪ)

another name for will-o'-the-wisp

Word Origin for ignis fatuus

C16: from Medieval Latin, literally: foolish fire
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012