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:

Calcar \Cal"car\, n. [L. calcaria lime kiln, fr. calx, calcis,
   lime. See Calx.] (Glass manuf.)
   A kind of oven, or reverberatory furnace, used for the
   calcination of sand and potash, and converting them into
   frit. --Ure.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Calcar \Cal"car\, n.; L. pl. Calcaria. [L., a spur, as worn on
   the heel, also the spur of a cock, fr. calx, calcis, the
   heel.]
   1. (Bot.) A hollow tube or spur at the base of a petal or
      corolla.
      [1913 Webster]

   2. (Zool.) A slender bony process from the ankle joint of
      bats, which helps to support the posterior part of the
      web, in flight.
      [1913 Webster]

   3. (Anat.)
      (a) A spur, or spurlike prominence.
      (b) A curved ridge in the floor of the leteral ventricle
          of the brain; the calcar avis, hippocampus minor, or
          ergot.
          [1913 Webster] Calcarate