The Collaborative International Dictionary of English v.0.48:

Ramadan \Ram`a*dan"\ (r[a^]m`[.a]*d[a^]n"), n. [Ar.
   rama[dsdot][=a]n, or ramaz[=a]n, properly, the hot month.]
   [Written also Ramadhan, Ramadzan, and Rhamadan.]
   1. The ninth Mohammedan month.
      [1913 Webster]

   2. The great annual fast of the Mohammedans, kept during
      daylight through the ninth month.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rhamadan \Rham`a*dan"\, n.
   See Ramadan.
   [1913 Webster]