i‧so‧therm/ˈaɪsəθɜːm $ -ɜːrm/ noun[COUNTABLE] technical [date : 1800-1900; Language : French; Origin : isotherme, from Greek iso- ( ⇨ iso-) + therme 'heat'] a line on a weather map joining places where the temperature is the same
noun EXAMPLES FROM CORPUS ▪ Aleksandrova rather confusingly calls the northern and southern belts arctic tundra and subarctic tundra, separating them by the 6°C July isotherm. ▪ An isotherm is a pressure-volume plot at constant temperature. ▪ Starting at Cape Sata in the far south, cherry trees burst into flower and a pink isotherm of blossoms sweeps northwards. ▪ The isotherm for CO2 at 321 K shows that the gas does not liquefy whatever the pressure or volume at this temperature. ▪ The boundary between the edge of the southern zone and the tundra is the 2°C July isotherm. ▪ The critical temperature of C02 is 304 K. The isotherm at this temperature is called the critical isotherm. ▪ The winter isotherm for this might well be above the next critical temperature for water, i.e. 30°C.