Adiabatic

adi;a;bat;ic pronunciation: function: adjective etymology: greek adiabatos impassable, from a- + diabatos passable, from diabainein to go across, from dia- + bainein to go — more at comedate: 1859 : occurring without loss or gain of heat lt;adiabatic expansion of a gasgt;— adi;a;bat;i;cal;ly adverb