Definition of ignis fatuus
plural ig·nes fat·ui play \-ˌnēz-ˈfa-chə-ˌwī\
1 : a light that sometimes appears in the night over marshy ground and is often attributable to the combustion of gas from decomposed organic matter
2 : a deceptive goal or hope
Origin of ignis fatuus
Medieval Latin, literally, foolish fire
First Known Use: 1563
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