Vendémiaire

Vendémiaire (French pronunciation: ​[vɑ̃demjɛʁ]) was the first month in the French Republican Calendar. The month was named after the Occitan word vendemiaire (grape harvester).

Vendémiaire was the first month of the autumn quarter (mois d'automne). It started on the day of the autumnal equinox, which fell between 22 September and 24 September, inclusive. It thus ended between 21 October and 23 October. It follows the Sansculottides of the past year and precedes Brumaire.

Like all FRC months Vendémiaire lasted 30 days and was divided into three 10-day weeks, called décades (decades). Every day had the name of an agricultural or ornamental plant, except the 5th (Quintidi) and 10th day (Decadi) of every decade, which had the name of a domestic animal (Quintidi) or an agricultural tool (Decadi).

...
Wikipedia