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.
Jack-o'-lantern \Jack"-o'-lan`tern\, Jack-with-a-lantern \Jack"-with-a-lan`tern\, n.
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(Biol.) A large orange-colored luminescent mushroom, Clitocybe illudens, also classified as Omphalotus olearius. It is poisonous and is sometimes found on hardwood tree stumps. [WordNet sense 1]
Syn: jack-a-lantern, Clitocybe illudens.
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a pale light sometimes seen at night over marshy ground; an ignis fatuus; a will-o'-the-wisp. [WordNet sense 2]``[Newspaper speculations] supplying so many more jack-o'-lanterns to the future historian.''
--Lowell.Syn: friar's lantern, ignis fatuus, will-o'-the-wisp.
A lantern carved from a hollowed-out pumpkin, with holes cut in the rind and so shaped that when it is illuminated by a candle inside, the features of a human face, cat's face, etc. appear in a glowing yellow color. It is used mostly as a decoration at Halloween.
Usage examples of "jack-with-a-lantern".
Jones continued his journey, contrary to the advice of Partridge, with what happened on that occasion They now discovered a light at some distance, to the great pleasure of Jones, and to the no small terror of Partridge, who firmly believed himself to be bewitched, and that this light was a Jack-with-a-lantern, or somewhat more mischievous.