The Collaborative International Dictionary of English v.0.48:

Isohyetose \I`so*hy"e*tose`\, a. [Iso- + Gr. "yeto`s rain.]
   (Phys. Geog.)
   Of or pertaining to lines connecting places on the earth's
   surface which have the same mean annual rainfall. -- n. An
   isohyetose line; called also isohyet.
   [1913 Webster]