The Collaborative International Dictionary of English v.0.48:

Mormon \Mor"mon\, prop. n. (Eccl.)
   One of a Christian denomination (The Church of Jesus Christ
   of Latter-day Saints) in the United States, followers of
   Joseph Smith, who professed to have found an addition to the
   Bible, engraved on golden plates, called the

   Book of Mormon, first published in 1830. The Mormons
      believe in polygamy, and their hierarchy of apostles,
      etc., has control of civil and religious matters.
      [1913 Webster +PJC]

   Note: The Mormons call their religious organization The
         Church of Jesus Christ of Latter-day Saints. Its head
         claims to receive revelations of God's will, and to
         have certain supernatural powers. The church
         headquarters are in Salt Lake City, Utah. They form a
         substantial fraction of the population of Utah, and at
         the end of the 20th centrury their numbers were
         increasing due to active proselytization.
         [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

Book of Mormon
    n 1: a sacred text revealed to Joseph Smith in 1830 by an
         ancient prophet Mormon; supposedly a record of ancient
         peoples of America translated by Joseph Smith