With my 'official legendary pedant' hat on

Thermidor [no E]

named after one of the months of the French Revolutionary Calendar

Autumn:
       Vendémiaire in French (from Latin vindemia, "grape harvest"), starting 22, 23 or 24 September
       Brumaire (from French brume, "fog"), starting 22, 23 or 24 October
       Frimaire (From French frimas, "frost"), starting 21, 22 or 23 November
    Winter:
       Nivôse (from Latin nivosus, "snowy"), starting 21, 22 or 23 December
       Pluviôse (from Latin pluvius, "rainy"), starting 20, 21 or 22 January
       Ventôse (from Latin ventosus, "windy"), starting 19, 20 or 21 February
    Spring:
       Germinal (from Latin germen, "germination"), starting 20 or 21 March
       Floréal (from Latin flos, "flower"), starting 20 or 21 April
       Prairial (from French prairie, "pasture"), starting 20 or 21 May
    Summer:
       Messidor (from Latin messis, "harvest"), starting 19 or 20 June
       Thermidor (or Fervidor) (from Greek thermon, "summer heat"), starting 19 or 20 July
       Fructidor (from Latin fructus, "fruit"), starting 18 or 19 August