"religious system revealed by Muhammad," 1816, from Arabic islam, literally "submission" (to the will of God), from root of aslama "he resigned, he surrendered, he submitted," causative conjunction of salima "he was safe," and related to salam "peace."
... Islam is the only major religion, along with Buddhism (if we consider the name of the religion to come from Budd, the Divine Intellect, and not the Buddha), whose name is not related to a person or ethnic group, but to the central idea of the religion. ["The Heart of Islam: Enduring Values for Humanity," Seyyed Hossein Nasr, 2002]
Earlier English names for the faith include Mahometry (late 15c.), Muhammadism (1610s), Islamism (1747), and Ismaelism (c. 1600; see Ismailite). The Ismailites were not numerous in Islam, but among them were the powerful Fatimid dynasty in Egypt and the Assassins, both of which loomed large in European imagination. This use also is in part from Ishmaelite, a name formerly given (especially by Jews) to Arabs, as descendants of Ishmael (q.v.).
"assimilated Christian in Moorish Spain," one who was allowed to continue practicing his religion in exchange for political allegiance, from Spanish Mozarabe "would-be Arab," from Arabic mostarib, from a desiderative verbal form of Arab. Related: Mozarabian (1706); Mozarabic.
"not to be spoken of, abominable, very shocking to the general sense of justice or religion," 1630s, from Latin nefandus "unmentionable, impious, heinous," from ne-, negative particle (see un- (1)), + fandus "to be spoken," gerundive of fari "to speak," from PIE root *bha- (2) "to speak, tell, say."
1560s, "person whose faith has been changed from one religion to another," from convert (v.). Earlier was convers (early 14c.), from Old French converse (n.). General (non-religious) sense of "person converted from one opinion or practice to another" is from 1640s.
