[1] : The Collaborative International Dictionary of English v.0.48

cesium \cesium\ n.
   the chemical element of atomic number 55. it is a univalent
   element, the most electropositive metal. symbol cs; atomic
   weight 132.905. it has a melting point of 28.4deg c.

   syn: caesium, cs.
        wordnet 1.5

[2] : WordNet (r) 2.0

cesium
     n : a soft silver-white ductile metallic element liquid at
         normal temperatures; the most electropositive and
         alkaline metal syn: caesium, cs, atomic number 55
see also:
caesium cs atomic number 55 

Cesium >> C Words
Cesium, definition of term: Cesium
cesium_pag1.html

Cesium 137 >> C Words
Cesium 137, definition of term: Cesium 137
cesium+137_pag1.html