Webster's New World College Dictionary:
n. an adherent of Islam
n. an advocate or supporter of Islamic, esp. orthodox Islamic, political rule
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The American Heritage Dictionary of the English Language, Fourth Edition:
n. 1. also Moslem. A believer in or adherent of Islam
"Islamist" (sub-entry of "Islamism"); "Islamism"
n. An Islamic revivalist movement, often characerized by moral conservaatism, literalism, and the attempt to impement Islamic values in all spheres of life. 2. The religious faith, principles, or cause of Islam.