Ignis Fatʹuus

means strictly a fatuous fire it is also called. “Jack o’ Lantern,” “Spunkie,” “Walking Fire,” “Will o’ the Wisp,” and “Fair Maid of Ireland.” Milton calls it Friar’s Lanthern, and Sir Walter Scott Friar Rush with a lantern. Morally speaking, a Uto’pian scheme, no more reducible to practice than the meteor so called can be turned to any useful end. (Plural, Ignes fatŭi.) (See Friar’s Lanthorn.)

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“When thou rannest up Gadshill in the night to catch my horse, if I did not think thou hadst been an ignis fatuous or a ball of wildfire, there’s no purchase in money.”—Shakespeare: 1 Henry IV., iii. 3.