thermometer: [17] Greek thérmē meant ‘heat’ (it came from prehistoric Indo-European *ghwerm-, *ghworm-, which probably also produced English warm). From it was formed French thermomètre (first recorded in 1624), which was borrowed into English in the early 1630s. The same source produced English therm [19] and thermal [18]; and thermos (from the related Greek thermós ‘hot’) was registered as a trademark for a vacuum flask in 1907. => warm
1630s, from French thermomètre (1620s), coined by Jesuit Father Jean Leuréchon from Greek thermos "hot" (see thermal) + metron "measure" (see meter (n.2)). An earlier, Latinate form was thermoscopium (1610s). The earliest such device was Galileo's air-thermometer, invented c. 1597. The typical modern version, with mercury in glass, was invented by Fahrenheit in 1714. Related: Thermometric; thermometrical.
