The Collaborative International Dictionary of English v.0.48:

Shah \Shah\ (sh[aum]), n. [Per. sh[=a]h a king, sovereign,
   prince. Cf. Checkmate, Chess, Pasha.]
   A former title of the supreme ruler in certain Eastern
   countries, especially Persia and Iran. [Written also
   schah.]
   [1913 Webster +PJC]

   Shah Nameh. [Per., Book of Kings.] A celebrated historical
      poem written by Firdousi, being the most ancient in the
      modern Persian language. --Brande & C.
      [1913 Webster]