The calendar adopted by the first French Republic in 1793 and abandoned in 1805; dates were calculated from Sept. 22, 1792 WordNet 3.0 & Open English WordNet

The French Republican calendar, also commonly called the French Revolutionary calendar, was a calendar created and implemented during the French Revolution, and used by the French government for about 12 years from late 1793 to 1805, and for 18 days by the Paris Commune in 1871, and meant to replace the Gregorian calendar. Wikipedia

Calendar Wikidata

The republican calendar used for twelve years in revolutionary France (from late 1793 to 1805). Wiktionary

Calendar used for twelve years in revolutionary France. Wiktionary (translation)