Merriam-Webster's Word of the Day for February 10, 2023 is: ignis fatuus \IG-nis FATCH-uh-wus\ noun

An ignis fatuus is a light that sometimes appears in the night over marshy ground and is often attributable to the combustion of gas from decomposed organic matter. The term can also refer to a deceptive goal or hope.

// An ignis fatuus hovered above the horizon as we made our late trek home.

// The film explores how people fall victim to the ignis fatuus of religious cults.

[See the entry >](https://www.merriam-webster.com/dictionary/ignis%20fatuus)

Examples:

"The flickering lights that led superstitious voyagers astray are not mere legends. So-called ignis fatuus, or 'foolish fire,' is a real phenomenon: a ball of flame that hovers above a marsh’s dark, still water for a few minutes before dissipating into the night." — Benji Jones, Popular Science, 31 Oct. 2018

Did you know?

Ignis fatuus is a Latin term meaning, literally, "foolish fire." Other names for this light are [jack-o'-lantern](https://www.merriam-webster.com/dictionary/jack-o%27-lantern) and [will-o'-the-wisp](https://www.merriam-webster.com/dictionary/will-o%27-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](https://www.merriam-webster.com/dictionary/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.