isopiestic lines

from The Collaborative International Dictionary of English v.0.48

Isopiestic \I`so*pi*es"tic\, a. [Iso- + Gr. ? to press.]
   (Thermodynamics)
   Having equal pressure.
   [1913 Webster]

   {Isopiestic lines}, lines showing, in a diagram, the
      relations of temperature and volume, when the elastic
      force is constant; -- called also {isobars}.
      [1913 Webster]