(variant form: also Muhammadan) is a term used as both a noun and an adjective meaning belonging or relating to either the religion of Islam or to that of its last prophet Muhammad. The term is now largely superseded by Muslim, Moslem or Islamic but was commonly used in Western literature until at least the mid 1960s. Muslim is more commonly used today than Moslem, and the term Mohammedan is generally considered archaic or in some cases even offensive. According to the SOED (1973), Mohammedan was in use by 1681, replacing the older term Mahometan that dates back to 1529.

The "Online Etymology Dictionary" reports that the earliest form in English of the name of Muhammad, was Mahum (c.1205) and originally used confusedly for "an idol." while that Wyclif has Macamethe (c.1380). Some medieval Christians in Western Europe believed that Muslims worshipped Mohammed(Mahomet) while others simply believed he was a Christian heretic. Still other Middle ages European literature often referred to Muslims as "pagans", or by sobriquets such as the paynim foe. These depictions such as those in the Song of Roland represent Muslims worshipping Muhammad as a god, and depict them worshipping various deities in the form of "idols", ranging from Apollo to Lucifer, but ascribing to them a chief deity known as "Termagant". When the Knights Templar were being tried for heresy reference was often made to their worship of a demon Baphomet, which was notable by implication for its similarity to the common rendition of Muhammad's name used by Christian writers of the time, Mahomet. All these and other variations on the theme were all set in the "temper of the times" of what was seen as a Muslim-Christian conflict as Medieval Europe was building a concept of "the great enemy" in the wake of the quickfire success of the Muslims through a series of conquests shortly after the fall of the Western Roman Empire, as well as the lack of real information in the West of the mysterious east.

Many Muslims object to the term, saying it implies that they worship their prophet Muhammad, in the manner Christians worship Christ. As Muhammed was traditionally regarded by Christians as a heresy, the label Mohammedanism (with many variant spellings) was traditionally used much as other heresies were named for their founders or leading teachers: Arianism for its founder Arius, Donatism for its founder Donatus Magnus, Eutychianism for its leading teacher Eutyches, Marcionism for its founder Marcion, Montanism for its founder Montanus, Nestorianism for its founder Nestorius, Pelagianism for its founder Pelagius, Priscillianism for its founder Priscillian, Sabellianism for its principal teacher Sabellius, Zoroastrianism for its prophet Zoroaster, and so forth. This way of referring to religious communities or sects is not normally controversial, as evidenced by Lutheranism, a term used by adherents and non-adherents alike, which has as nothing to do with a deification or worship of Martin Luther, and involves rather less of a cult of personality or veneration for Luther than Islamic veneration for Muhammad.

Some Qur'an Alone followers, objecting to the mainstream Muslim practice of upholding hadith and sunnah of Muhammad, and adding of Mohammad's name to the shahadah, use the term to describe orthodox Muslims with the intention to imply a worship of Mohammad.