The Collaborative International Dictionary of English v.0.48:

Barium \Ba"ri*um\, n. [NL., fr. Gr. bary`s heavy.] (Chem.)
   One of the elements, belonging to the alkaline earth group; a
   metal having a silver-white color, and melting at a very high
   temperature. It is difficult to obtain the pure metal, from
   the facility with which it becomes oxidized in the air.
   Atomic weight, 137. Symbol, Ba. Its oxide called baryta.
   [Rarely written barytum.]
   [1913 Webster]

   Note: Some of the compounds of this element are remarkable
         for their high specific gravity, as the sulphate,
         called heavy spar, and the like. The oxide was called
         barote, by Guyton de Morveau, which name was changed by
         Lavoisier to baryta, whence the name of the metal.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Barytum \Ba*ry"tum\, n. [NL.] (Chem.)
   The metal barium. See Barium. [R.]
   [1913 Webster]