The Collaborative International Dictionary of English v.0.48:

Hippocampus \Hip`po*cam"pus\, n. [L., the sea horse, Gr. ? a
   hippocampus (in senses 1 and 2); "i`ppos horse + ? to bend.]
   1. (Class. Myth.) A fabulous monster, with the head and fore
      quarters of a horse joined to the tail of a dolphin or
      other fish (Hippocampus brevirostris), -- seen in
      Pompeian paintings, attached to the chariot of Neptune.
      --Fairholt.
      [1913 Webster]

   2. (Zool.) A genus of lophobranch fishes of several species
      in which the head and neck have some resemblance to those
      of a horse; -- called also sea horse.
      [1913 Webster]

   Note: They swim slowly, in an erect position, and often cling
         to seaweeds by means of the incurved prehensile tail.
         The male has a ventral pouch, in which it carries the
         eggs till hatched.
         [1913 Webster]

   3. (Zool.) A name applied to either of two ridges of white
      matter in each lateral ventricle of the brain. The larger
      is called hippocampus major or simply hippocampus. The
      smaller, hippocampus minor, is called also ergot and
      calcar.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ergot \Er"got\, n. [F. ergot, argot, lit., a spur.]
   1. A diseased condition of rye and other cereals, in which
      the grains become black, and often spur-shaped. It is
      caused by a parasitic fungus, Claviceps purpurea.
      [1913 Webster]

   2. The mycelium or spawn of this fungus infecting grains of
      rye and wheat. It is a powerful remedial agent, and also a
      dangerous poison, and is used as a means of hastening
      childbirth, and to arrest bleeding.
      [1913 Webster]

   3. (Far.) A stub, like soft horn, about the size of a
      chestnut, situated behind and below the pastern joint.
      [1913 Webster]

   4. (Anat.) See 2d Calcar, 3
      (b) .
          [1913 Webster]

WordNet (r) 3.0 (2006):

ergot
    n 1: a plant disease caused by the ergot fungus
    2: a fungus that infects various cereal plants forming compact
       black masses of branching filaments that replace many grains
       of the plant; source of medicinally important alkaloids and
       of lysergic acid [syn: ergot, Claviceps purpurea]