The Collaborative International Dictionary of English v.0.48:

May \May\, n. [F. Mai, L. Maius; so named in honor of the
   goddess Maia (Gr. Mai^a), daughter of Atlas and mother of
   Mercury by Jupiter.]
   1. The fifth month of the year, containing thirty-one days.
      --Chaucer.
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   2. The early part or springtime of life.
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            His May of youth, and bloom of lustihood. --Shak.
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   3. (Bot.) The flowers of the hawthorn; -- so called from
      their time of blossoming; also, the hawthorn.
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            The palm and may make country houses gay. --Nash.
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            Plumes that mocked the may.           --Tennyson.
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   4. The merrymaking of May Day. --Tennyson.
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   Italian may (Bot.), a shrubby species of Spiraea
      (Spiraea hypericifolia) with many clusters of small
      white flowers along the slender branches.

   May apple (Bot.), the fruit of an American plant
      (Podophyllum peltatum). Also, the plant itself
      (popularly called mandrake), which has two lobed leaves,
      and bears a single egg-shaped fruit at the forking. The
      root and leaves, used in medicine, are powerfully drastic.


   May beetle, May bug (Zool.), any one of numerous species
      of large lamellicorn beetles that appear in the winged
      state in May. They belong to Melolontha, and allied
      genera. Called also June beetle.

   May Day, the first day of May; -- celebrated in the rustic
      parts of England by the crowning of a May queen with a
      garland, and by dancing about a May pole.

   May dew, the morning dew of the first day of May, to which
      magical properties were attributed.

   May flower (Bot.), a plant that flowers in May; also, its
      blossom. See Mayflower, in the vocabulary.

   May fly (Zool.), any species of Ephemera, and allied
      genera; -- so called because the mature flies of many
      species appear in May. See Ephemeral fly, under
      Ephemeral.

   May game, any May-day sport.

   May lady, the queen or lady of May, in old May games.

   May lily (Bot.), the lily of the valley (Convallaria
      majalis).

   May pole. See Maypole in the Vocabulary.

   May queen, a girl or young woman crowned queen in the
      sports of May Day.

   May thorn, the hawthorn.
      [1913 Webster]

WordNet (r) 3.0 (2006):

May queen
    n 1: the girl chosen queen of a May Day festival [syn: May
         queen, queen of the May]