Source : Webster's Revised Unabridged Dictionary (1913)

OEil-de-boeuf \[OE]il`-de-b[oe]uf"\, n.; pl.
   {[OE]ils-de-b[oe]uf}. [F., lit., eye of an ox.] (Arch.)
   A circular or oval window; -- generally used of architecture
   of the 17th and 18th centuries. A famous room in the palace
   of Versailles bears this name, from the oval window opening
   into it.