The Collaborative International Dictionary of English v.0.48:

Wicca \Wic"ca\ (w[i^]k"k[.a]), prop. n. [OE. wicche wizard, AS.
   wicce, fem., wicca, masc.; see also witch and wicked.]
   1. A religion derived from pre-Christian times, also called
      Witchcraft[4], which practices a benevolent reverence
      for nature, and recognizes two deities, variously viewed
      as Mother & Father, Goddess & God, Female & Male, etc.;
      its practitioners are called Wiccans, Wiccas, or witches.
      Since there is no central authority to propagate dogma,
      the beliefs and practices of Wiccans vary significantly.
      [PJC]

            Encouraged by court rulings recognizing witchcraft
            as a legal religion, an increasing number of books
            related to the subject, and the continuing cultural
            concern for the environment, Wicca -- as
            contemporary witchcraft is often called -- has been
            growing in the United States and abroad. It is a
            major element in the expanding "neo-pagan" movement
            whose members regard nature itself as charged with
            divinity.                             --Gustav
                                                  Niebuhr (N. Y.
                                                  Times, Oct.
                                                  31, 1999, p.
                                                  1)
      [PJC]

            "I don't worship Satan, who I don't think exists,
            but I do pray to the Goddess of Creation." said
            Margot S. Adler, a New York correspondent for
            National Public Radio and a Wiccan practitioner.
            "Wicca is not anti-Christian or pro-Christian, it's
            pre-Christian."                       --Anthony
                                                  Ramirez (N. Y.
                                                  Times Aug. 22,
                                                  1999, p. wk 2)
      [PJC]

   Note: Wicca is a ditheistic religion, also called Witchcraft,
         founded on the beliefs and doctrines of pre-Roman
         Celts, including the reverence for nature and the
         belief in a universal balance. Though frequently
         practiced in covens, solitary practitioners do exist.
         The modern form of the religion was popularized in 1954
         by Gerald Gardener's Witchcraft Today. It is viewed as
         a form of neo-paganism.
         Wicca recognizes two deities, visualized as Mother &
         Father, Goddess & God, Female & Male, etc. These
         dieties are nameless, but many Wiccans adopt a name
         with which they refer to the two: Diana is a popular
         name for the Goddess to take, among others such as
         Artemis, Isis, Morrigan, etc. Some of her symbols are:
         the moon; the ocean; a cauldron; and the labrys
         (two-headed axe), among others. The God is of equal
         power to the Goddess, and takes on names such as
         Apollo, Odin, Lugh, etc. A small number of his symbols
         are: the sun; the sky; a horn (or two horns); and
         others.
         Witchcraft is not a Christian denomination; there is no
         devil in its mythos, thus the devil cannot be
         worshiped, and the medieval view of Witches as
         Satan-worshipers is erroneous. Satanists are not
         Witches and Witches are not Satanists. Both have a
         tendency to be offended when the two are confused.
         In the Wiccan religion male Witches are not "Warlocks".
         The term Warlock comes from Scottish, meaning
         'oathbreaker', 'traitor', or 'devil'. Its application
         to male witches is of uncertain origin.
         The Wiccan Rede, "An it harm none, do what thou wilt"
         comes in many variations. All of them say the same
         thing, "Do as you wish, just don't do anything to harm
         anyone." It is implied that 'anyone' includes one's
         self.
         Witches practice in groups called Covens or as solitary
         practitioners, and some practice "magic", which is to
         say, they pray. Since the one rule that Witches have
         requires that they can not do harm, harmful magic does
         not exist in Wicca. In Wicca, "magic" is simply subtly
         altering small things, to gain a desired effect.
         Wicca, sometimes called Neo-Witchcraft, was revived in
         the 1950s, when the last laws against Witchcraft were
         repealed. Gerald Gardner founded Gardnerian Wicca
         sometime after his book, Witchcraft Today, was
         published in 1954. Raymond Buckland, in America, did
         much the same that Gardner did in Europe -- stood up to
         the misconceptions about Witchcraft.
         Two other books describing the modern practice of Wicca
         are:
         Wicca: A Guide for the Solitary Practitioner, by Scott
         Cunningham, Llewellyn Publications, 1988.
         Buckland's Complete Book of Witchcraft, by Raymond
         Buckland, Llewellyn Publications, 1975.
         A Web site devoted to elucidation of modern witchcraft
         is:
         [a href="http:]/www.witchvox.com">Witchvox --Cody Scott
         [PJC]

   2. A practitioner of Wicca, also commonly called a Wiccan,
      Wicca, or witch .
      [PJC]

            For at least one person who has seen "The Blair
            Witch Project", the surprise hit movie of the summer
            did not so much terrify as infuriate. One long slur
            against witches, said Selena Fox, a witch, or Wicca,
            as male and female American witches prefer to call
            themselves.                           --Anthony
                                                  Ramirez (N. Y.
                                                  Times, Aug.
                                                  22, 1999, p.
                                                  wk 2)
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Wiccan \Wic"can\ (w[i^]k"k[i^]n), prop. a.
   Of, pertaining to, or characteristic of, Wicca or its
   adherents.
   [PJC]

The Collaborative International Dictionary of English v.0.48:

Wiccan \Wic"can\ (w[i^]k"k[i^]n), prop. n.
   An adherent or practitioner of Wicca.
   [PJC]

WordNet (r) 3.0 (2006):

Wiccan
    adj 1: of or relating to Wicca
    n 1: a believer in Wicca [syn: Wiccan, witch]