The Collaborative International Dictionary of English v.0.48:
Thermidor \Ther`mi`dor"\, n. [F., fr. Gr. ? warm, hot.] The eleventh month of the French republican calendar, -- commencing July 19, and ending August 17. See the Note under Vend['e]miaire. [1913 Webster]WordNet (r) 3.0 (2006):
Thermidor n 1: eleventh month of the Revolutionary calendar (July and August); the month of heat