The Collaborative International Dictionary of English v.0.48:

Cryohydrate \Cry`o*hy"drate\ (kr?`?-h?"dr?t), n. [Gr. kry`os
   cold + E. hydrate.] (Chem.)
   A substance, as salt, ammonium chloride, etc., which
   crystallizes with water of crystallization only at low
   temperatures, or below the freezing point of water. -- F.
   Guthrie.
   [1913 Webster]