ignisfatuus

ig·nis fat·u·us (ĭgʹnĭs făchʹo͞o-əs) n. pl. ig·nes fat·u·i (ĭgʹnēz făchʹo͞o-ī')

1. A phosphorescent light that hovers or flits over swampy ground at night, possibly caused by spontaneous combustion of gases emitted by rotting organic matter. Also called friar's lantern, jack-o'-lantern, will-o'-the-wisp, wisp.

2. Something that misleads or deludes; an illusion.

  [Medieval Latin : Latin ignis, fire + Latin fatuus, foolish.]

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