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.