April fool, n. The March fool with another month added to his folly.

Ambrose Bierce coined this definition in his satirical lexicon The Devil’s Dictionary, a work he published in newspaper installments in the late 19th century before it appeared in book form. Bierce, a journalist and veteran of the American Civil War, became famous for his caustic wit and for skewering social conventions through mock “dictionary” entries. The entry for “April fool” draws on the popular custom of April Fools’ Day pranks, but Bierce reframes it as evidence of human credulity and persistent stupidity—suggesting that folly is not confined to a single day, but merely continues from month to month.

Bierce’s joke works by treating “April fool” as a definable type rather than a temporary victim of a prank. By calling him “The March fool with another month added to his folly,” Bierce implies that foolishness is cumulative and habitual: time does not cure it, it compounds it. The definition also punctures the mild, festive tone of April Fools’ Day by suggesting that the real butt of the joke is not the tricked person on April 1, but the enduring human tendency to be duped. In Bierce’s worldview, society’s rituals merely provide new occasions to display the same old gullibility.