isothermal

Of, relating to, or indicating equal or constant temperatures.

Of or designating changes of pressure and volume at constant temperature.

Of or relating to an isotherm.

An isotherm.

In crystallography, applied to the lines on a crystal face, or more generally to the surfaces in a crystal, which measure the rate of heat-conductivity, these lines or surfaces being characterized by equal degrees of temperature when heat is applied at a certain point.