I'so-di'a-bāt'ic, a.

a. [Gr. ἴσος, equal, and διαβαίνειν, to pass through.] (Thermodynamics.) Pertaining to the reception or giving out of equal quantities of heat by a substance. Rankine.

Isodiabatic lines, or curves, a pair of lines or curves exhibiting, on a diagram of energy, the law of variation of the pressure and density of a fluid, the one during the lowering, and the other during the raising, of its temperature, when the quantity of heat given out by the fluid during any given stage of the one process is equal to the quantity received during the corresponding stage of the other. Such lines are said to be isodiabatic with respect to each other.

An adiabatic line is one exhibiting the variations of pressure and volume of a fluid when it expands without either receiving or giving out heat. Rankine.