The Collaborative International Dictionary of English v.0.48:

Muzarab \Muz"a*rab\, n. [Sp. mozarabe, fr. Ar. mosta'rib, a name
   applied to strange tribes living among the Arabs.] (Eccl.
   Hist.)
   One of a denomination of Christians formerly living under the
   government of the Moors in Spain, and having a liturgy and
   ritual of their own. [Written also Mozarab, Mostarab.]
   --Brande & C.
   [1913 Webster]