\Ad`i*a*bat"ic\, a. [Gr. ? not passable; 'a priv. + ?
through + ? to go.] (Physics)
Not giving out or receiving heat. -- {Ad`i*a*bat`ic*al*ly},
adv.
{Adiabatic line} or {curve}, a curve exhibiting the
   variations of pressure and volume of a fluid when it
   expands without either receiving or giving out heat.
   --Rankine.