ignis fatuus
noun
Did you know?
Ignis fatuus is a Latin term meaning, literally, "foolish fire." Other names for this light are jack-o'-lantern and will-o'-the-wisp—both of which are connected to folklore about mysterious men, Jack and Will, who carry a lantern or a wisp of light at night. A Scottish name for ignis fatuus is spunkie, from spunk, meaning "spark" or "a small fire." It has also been told that ignes fatui (the Latin plural form) are roaming souls. No doubt these stories spooked listeners by candlelight, but in time, advancements in science not only gave us electricity to dispel the darkness but proved ignis fatuus to be a visible exhalation of gas from the ground, which is rarely seen today.
Examples of ignis fatuus in a Sentence
Fox News, 3 Mar. 2023
The story also helped explain ignis fatuus, a natural phenomenon that occurs in marshlands and bogs—such as those in Ireland’s countryside—producing flickering lights as gases from decomposing organic matter combust.
—National Geographic, 27 Oct. 2020
Cite this Entry
“Ignis fatuus.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/ignis%20fatuus. Accessed 31 Oct. 2025.
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