Source : Webster's Revised Unabridged Dictionary (1913)

Cabochon \Ca`bo`chon"\ (k[.a]`b[-o]`sh[^o]N"), n. [F.] (Jewelry)
   A stone of convex form, highly polished, but not faceted;
   also, the style of cutting itself. Such stones are said to be
   cut en cabochon.

Source : WordNet®

cabochon
     n : a highly polished convex-cut but unfaceted gem