NOUN (2)

1. the ninth month of the Islamic calendar; the month of fasting; the holiest period for the Islamic faith;

2. (Islam) a fast (held from sunrise to sunset) that is carried out during the Islamic month of Ramadan;

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]

WordNet (r) 3.0 (2006):

Ramadan
    n 1: the ninth month of the Islamic calendar; the month of
         fasting; the holiest period for the Islamic faith
    2: (Islam) a fast (held from sunrise to sunset) that is carried
       out during the Islamic month of Ramadan