Source : Webster's Revised Unabridged Dictionary (1913)

Diadem \Di"a*dem\, n. [F. diad[`e]me, L. diadema, fr. Gr. ?, fr.
   ? to bind round; dia` through, across + ? to bind; cf. Skr.
   d[=a] to bind.]
   1. Originally, an ornamental head band or fillet, worn by
      Eastern monarchs as a badge of royalty; hence (later),
      also, a crown, in general. ``The regal diadem.'' --Milton.

   2. Regal power; sovereignty; empire; -- considered as
      symbolized by the crown.

   3. (Her.) An arch rising from the rim of a crown (rarely also
      of a coronet), and uniting with others over its center.

   {Diadem lemur}. (Zo["o]l.) See {Indri}.

   {Diadem spider} (Zo["o]l.), the garden spider.