From WordNet (r) 3.0 (2006) [wn]:
hippocampus
n 1: a complex neural structure (shaped like a sea horse)
consisting of grey matter and located on the floor of each
lateral ventricle; intimately involved in motivation and
emotion as part of the limbic system; has a central role in
the formation of memories
2: seahorses [syn: Hippocampus, genus Hippocampus]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
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]