Revolutionary calendar

WordReference Random House Unabridged Dictionary of American English © 2025

Revolu′tionary cal′endar, 

1. World History the calendar of the French First Republic, adopted in 1793 and abandoned in 1805, consisting of 12 months, each of 30 days, and 5 intercalary days added at the end of the year (6 every fourth year). The months, beginning at the autumnal equinox, are Vendémiaire, Brumaire, Frimaire, Nivôse, Pluviôse, Ventôse, Germinal, Floréal, Prairial, Messidor, Thermidor, and Fructidor.

Collins Concise English Dictionary © HarperCollins Publishers::

Revolutionary calendar noun

1. the calendar adopted by the French First Republic in 1793 and abandoned in 1805. Dates were calculated from Sept 22, 1792. The months were called Vendémiaire, Brumaire, Frimaire, Nivôse, Pluviôse, Ventôse, Germinal, Floréal, Prairial, Messidor, Thermidor, and Fructidor