ignis fatuus Meaning, Definition & Usage

  1. noun a pale light sometimes seen at night over marshy ground
    friar's lantern; jack-o'-lantern; will-o'-the-wisp.
  2. noun an illusion that misleads
    will-o'-the-wisp.

WordNet

Ig"nis fat"u*us
Etymology
L. ignis fire + fatuus foolish. So called in allusion to its tendency to mislead travelers.
Wordforms
plural Ignes fatui
Definitions
  1. A phosphorescent light that appears, in the night, over marshy ground, supposed to be occasioned by the decomposition of animal or vegetable substances, or by some inflammable gas; -- popularly called also Will-with-the-wisp, or Will-o'-the-wisp, and Jack-with-a-lantern, or Jack-o'-lantern. thought to be caused by phosphine, PH3, a sponaneously combustible gas.
  2. Fig.: A misleading influence; a decoy.
    Scared and guided by the ignis fatuus of popular superstition. Jer. Taylor.

Webster 1913