friar's lantern, ignis fatuus, Also called: jack-o'-lantern a pale flame or phosphorescence sometimes seen over marshy ground at night. It is believed to be due to the spontaneous combustion of methane or other hydrocarbons originating from decomposing organic matter
2.
a person or thing that is elusive or allures and misleads
[C17: originally Will with the wisp, from Will short for William and wisp in former sense of a twist of hay or straw burning as a torch]
a calculus or concretion found in the stomach or intestines of certain animals, esp. ruminants, formerly reputed to be an effective remedy for poison.
an extraordinary or unusual thing, person, or event; an exceptional example or instance.
a printed punctuation mark (‽), available only in some typefaces, designed to combine the question mark (?) and the exclamation point (!), indicating a mixture of query and interjection, as after a rhetorical question.