The Collaborative International Dictionary of English v.0.48:

Islam \Is"lam\, n. [Ar. isl[=a]m obedience to the will of God,
   submission, humbling one's self, resigning one's self to the
   divine disposal. Cf. Moslem.]
   [1913 Webster]
   1. The religion of the Mohammedans; Mohammedanism; Islamism.
      Their formula of faith is: There is no God but Allah, and
      Mohammed is his prophet.
      [1913 Webster]

   2. The whole body of Mohammedans, or the countries which they
      occupy.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Mohammedanism \Mo*ham"med*an*ism\, Mohammedism \Mo*ham"med*ism\
,  prop. n.
   The religion, or doctrines and precepts, of Mohammed,
   contained in the Koran; Islamism; Islam. The term Islam is
   preferred by most Moslems, and some find the term
   Mohammedanism to be offensive, as they worship Allah, not
   Mohammed.
   [1913 Webster +PJC] Mohammedanize

WordNet (r) 3.0 (2006):

Islam
    n 1: the civilization of Muslims collectively which is governed
         by the Muslim religion; "Islam is predominant in northern
         Africa, the Middle East, Pakistan, and Indonesia" [syn:
         Islam, Muslimism]
    2: the monotheistic religious system of Muslims founded in
       Arabia in the 7th century and based on the teachings of
       Muhammad as laid down in the Koran; "Islam is a complete way
       of life, not a Sunday religion"; "the term Muhammadanism is
       offensive to Muslims who believe that Allah, not Muhammad,
       founded their religion" [syn: Islam, Islamism,
       Mohammedanism, Muhammadanism, Muslimism]