- 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; Also called will-o'-the-wisp, wisp.
- Something that misleads or deludes; an illusion.
[Medieval Latin : Latin ignis, fire + Latin fatuus, foolish.]







