The Collaborative International Dictionary of English v.0.48:

Coral \Cor"al\, n. [Of. coral, F, corail, L. corallum, coralium,
   fr. Gr. kora`llion.]
   1. (Zool.) The hard parts or skeleton of various Anthozoa,
      and of a few Hydrozoa. Similar structures are also formed
      by some Bryozoa.
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   Note: The large stony corals forming coral reefs belong to
         various genera of Madreporaria, and to the hydroid
         genus, Millepora. The red coral, used in jewelry, is
         the stony axis of the stem of a gorgonian (Corallium
         rubrum) found chiefly in the Mediterranean. The fan
         corals, plume corals, and sea feathers are species
         of Gorgoniacea, in which the axis is horny.
         Organ-pipe coral is formed by the genus Tubipora, an
         Alcyonarian, and black coral is in part the axis of
         species of the genus Antipathes. See Anthozoa,
         Madrepora.
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   2. The ovaries of a cooked lobster; -- so called from their
      color.
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   3. A piece of coral, usually fitted with small bells and
      other appurtenances, used by children as a plaything.
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   Brain coral, or Brain stone coral. See under Brain.

   Chain coral. See under Chain.

   Coral animal (Zool.), one of the polyps by which corals are
      formed. They are often very erroneously called coral
      insects.

   Coral fish. See in the Vocabulary.

   Coral reefs (Phys. Geog.), reefs, often of great extent,
      made up chiefly of fragments of corals, coral sands, and
      the solid limestone resulting from their consolidation.
      They are classed as fringing reefs, when they border the
      land; barrier reefs, when separated from the shore by a
      broad belt of water; atolls, when they constitute
      separate islands, usually inclosing a lagoon. See Atoll.


   Coral root (Bot.), a genus (Corallorhiza) of orchideous
      plants, of a yellowish or brownish red color, parasitic on
      roots of other plants, and having curious jointed or
      knotted roots not unlike some kinds of coral. See Illust.
      under Coralloid.

   Coral snake. (Zo)
      (a) A small, venomous, Brazilian snake (Elaps
          corallinus), coral-red, with black bands.
      (b) A small, harmless, South American snake (Tortrix
          scytale).

   Coral tree (Bot.), a tropical, leguminous plant, of several
      species, with showy, scarlet blossoms and coral-red seeds.
      The best known is Erythrina Corallodendron.

   Coral wood, a hard, red cabinet wood. --McElrath.
      [1913 Webster]

WordNet (r) 3.0 (2006):

coral root
    n 1: a wildflower of the genus Corallorhiza growing from a hard
         mass of rhizomes associated with a fungus that aids in
         absorbing nutrients from the forest floor