isothermal

a. [ Cf. F. isotherme. ] (a) Relating to equality of temperature, or an isotherm. (b) (Phys. Geog.) Having reference to the geographical distribution of temperature, as exhibited by means of isotherms; as, an isothermal line; an isothermal chart. [ 1913 Webster ]

Isothermal line. (a) An isotherm. (b) A line drawn on a diagram of energy such that its ordinates represent the pressures of a substance corresponding to various volumes, while the absolute temperature is maintained at a constant value. --
Isothermal zones, spaces on opposite sides of the equator having the same mean temperature, and bounded by corresponding isothermal lines. [ 1913 Webster ]