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