The Collaborative International Dictionary of English v.0.48:

Vilayet \Vi`la*yet"\, n. [Turk., from Ar. wil[=a]yah.]
   One of the chief administrative divisions or provinces of the
   Ottoman Empire; -- formerly called eyalet.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Eyalet \E`ya*let"\, n. [Turk., fr. Ar. iy[=a]lah.]
   Formerly, one of the administrative divisions or provinces of
   the Ottoman Empire; -- now called a vilayet.
   [1913 Webster]