The Collaborative International Dictionary
Ignis fatuus \Ig"nis fat"u*us\; pl. Ignes fatui. [L. ignis fire + fatuus foolish. So called in allusion to its tendency to mislead travelers.]
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.
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Fig.: A misleading influence; a decoy.
Scared and guided by the ignis fatuus of popular superstition.
--Jer. Taylor.
Usage examples of "ignes fatui".
Out in the surrounding marshland, the ignes fatui were lighting their own lamps, wispy blobs of methane blue, firefly glimmerings that winked on and off in scattered synchrony, wandering pale flames gliding around the island's misty backwaters like lost elfin boats.
Upon the whole, no person could be less liable than myself to be led away from the severe precincts of truth by the ignes fatui of superstition.