Thermidor (French pronunciation: ​[tɛʁmidɔʁ]) was the eleventh month in the French Republican Calendar. The month was named after the French word thermal, derived from the Greek word "thermos" (heat).

Thermidor was the second month of the summer quarter (mois d'été). It started July 19 or 20. It ended August 17 or 18. It follows the Messidor and precedes the Fructidor. During Year 2, it was sometimes called Fervidor.

Because of the Thermidorian Reaction—9 Thermidor Year II—the overthrow of revolutionary radical Maximilien Robespierre and his followers in that month, the word "Thermidor" has come to mean a retreat from more radical goals and strategies during a revolution, especially when caused by a replacement of leading personalities.