Source : Webster's Revised Unabridged Dictionary (1913)

Adiabatic \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.

Source : WordNet®

adiabatic
     adj : occurring without loss or gain of heat; "adiabatic
           expansion" [ant: {diabatic}]