What does Boxing Day have to do with boxing?
1826 (adj.); 1852 (n.), from French isotherme (see isotherm) + -al (1).
isothermal i·so·ther·mal (ī'sə-thûr'məl)adj. Of, relating to, or indicating equal or constant temperatures.
Relating to or indicating equal or constant temperatures.
Relating to a process, usually changes of pressure and volume, occurring at a constant temperature and following Boyle's Law.
Relating to an isotherm.