The Collaborative International Dictionary of English v.0.48:

Mohammed \Mohammed\ (m[=o]*h[a^]m"m[e^]d) n. ['The praised
   one'.] [Also spelled Mahomed, Mahomet, Muhammad (the
   Arabic form), Mahmoud, Mehemet, etc.]
   The prophet who founded Islam (570-632).

   Syn: Muhammad, Mahomet, Mahmoud.
        [WordNet 1.5] Mohammed (or Mahomet (ma*hom"et)) was born
        at Mecca, Arabia, about 570: died at Medina, Arabia,
        June 8, 632. He was the founder of Mohammedanism, or
        Islam ('surrender,' namely, to God). He was the
        posthumous son of Abdallah by his wife Amina, of the
        family of Hashim, the noblest among the Koreish, and was
        brought up in the desert among the Banu Saad by a
        Bedouin woman named Halima. At the age of six he lost
        his mother, and at eight his grandfather, when he was
        cared for by his uncle Abu-Talib. When about twelve
        years old (582) he accompanied a caravan to Syria, and
        may on this occasion have come for the first time in
        contact with Jews and Christians. A few years later he
        took part in the "sacrilegious war" (so called because
        carried on during the sacred months, when fighting was
        forbidden) which raged between the Koreish and the Banu
        Hawazin 580-590. He attended sundry preachings and
        recitations at Okatz, which may have awakened his
        poetical and rhetorical powers and his religious
        feelings; and for some time was occupied as a shepherd,
        to which he later refers as being in accordance with his
        career as a prophet, even as it was with that of Moses
        and David. When twenty-five years old he entered the
        service of the widow Khadijah, and made a second journey
        to Syria, on which he again had an opportunity to come
        in frequent contact with Jews and Christians, and to
        acquire some knowledge of their religious teachings. He
        soon married Khadijah, who was fifteen years his senior.
        Of the six children which she bore him, Fatima became
        the most famous. In 605 he attained some influence in
        Mecca by settling a dispute about the rebuilding of the
        Kaaba. The impressions which he had gathered from his
        contact with Judaism and Christianity, and from Arabic
        lore, began now strongly to engage his mind. He
        frequently retired to solitary places, especially to the
        cave of Mount Hira, north of Mecca. He passed at that
        time (he was then about forty years old) through great
        mental struggles, and repeatedly meditated suicide. It
        must have been during these lonely contemplations that
        the yearnings for a messenger from God for his people,
        and the thought that he himself might be destined for
        this mission, were born in his ardent mind. During one
        of his reveries, in the month of Ramadan, 610, he beheld
        in sleep the angel Gabriel, who ordered him to read from
        a scroll which he held before him the words which begin
        the 96th sura (chapter) of the Koran. After the lapse of
        some time, a second vision came, and then the
        revelations began to follow one another frequently. His
        own belief in his mission as apostle and prophet of God
        was now firmly established. The first convert was his
        wife Khadijah, then followed his cousin and adopted son
        Ali, his other adopted son Zeid, and Abu-Bekr, afterward
        his father-in-law and first successor (calif). Gradually
        about 60 adherents rallied about him. But after three
        years' preaching the mass of the Meccans rose against
        him, so that part of his followers had to resort to
        Abyssinia for safety in 614. This is termed the first
        hejira. Mohammed in the meanwhile continued his meetings
        in the house of one of his disciples, Arqaan, in front
        of the Kaaba, which later became known as the "House of
        Islam." At one time he offered the Koreish a compromise,
        admitting their gods into his system as intercessors
        with the Supreme Being, but, becoming
        conscience-stricken, took back his words. The conversion
        of Hamza and Omar and 39 others in 615-616 strengthened
        his cause. The Koreish excommunicated Mohammed and his
        followers, who were forced to live in retirement. In
        620, at the pilgrimage, he won over to his teachings a
        small party from Medina. In Medina, whither a teacher
        was deputed, the new religion spread rapidly. To this
        period belongs the vision or dream of the miraculous
        ride, on the winged horse Borak, to Jerusalem, where he
        was received by the prophets, and thence ascended to
        heaven. In 622 more than 70 persons from Medina bound
        themselves to stand by Mohammed. The Meccans proposed to
        kill him, and he fled on the 20th of June, 622, to
        Medina. This is known as the hejira ('the flight'), and
        marks the beginning of the Mohammedan era. This event
        formed a turning-point in the activity of Mohammed. He
        was thus far a religious preacher and persuader; he
        became in his Medinian period a legislator and warrior.
        He built there in 623 the first mosque, and married
        Ayesha. In 624 the first battle for the faith took place
        between Mohammed and the Meccans in the plain of Bedr,
        in which the latter were defeated. At this time, also,
        Mohammed began bitterly to inveigh against the Jews, who
        did not recognize his claims to be the "greater prophet"
        promised by Moses. He changed the attitude of prayer
        (kibla) from the direction of Jerusalem to that of the
        Kaaba in Mecca, appointed Friday as the day for public
        worship, and instituted the fast of Ramadan and the
        tithe or poor-rate. The Jewish tribe of the Banu
        Kainuka, settled at Medina, was driven out; while of
        another Jewish tribe, the Banu Kuraiza, all the men, 700
        in number, were massacred. In 625 Mohammed and his
        followers were defeated by the Meccans in the battle of
        Ohud. The following years were filled out with
        expeditions. One tribe after another submitted to
        Mohammed, until in 631 something like a definite
        Mohammedan empire was established. In 632 the prophet
        made his last pilgrimage to Mecca, known as the
        "farewell pilgrimage," or the pilgrimage of the
        "announcement" or of "Islam." In the same year he died
        while planning an expedition against the frontier of the
        Byzantine empire. Mohammed was a little above the middle
        height, of a commanding figure, and is described as
        being of a modest, tender, and generous disposition. His
        manner of life was very simple and frugal. He mended his
        own clothes, and his common diet was barley-bread and
        water. But he enjoyed perfumes and the charms of women.
        His character appears composed of the strongest
        inconsistencies. He could be tender, kind, and liberal,
        but on occasions indulged in cruel and perfidious
        assassinations. With regard to his prophetic claims, it
        is as difficult to assume that he was sincere
        throughout, or self-deceived, as that he was throughout
        an impostor. In his doctrines there is practically
        nothing original. The legends of the Koran are chiefly
        drawn from the Old Testament and the rabbinical
        literature, which Mohammed must have learned from a Jew
        near Mecca, though he presents them as original
        revelations by the angel Gabriel, See Koran.
        [Century Dict. 1906]

WordNet (r) 3.0 (2006):

Muhammad
    n 1: leader of Black Muslims who campaigned for independence for
         Black Americans (1897-1975) [syn: Muhammad, Elijah
         Muhammad]
    2: the Arab prophet who, according to Islam, was the last
       messenger of Allah (570-632) [syn: Mohammed, Mohammad,
       Muhammad, Mahomet, Mahound]