Hippocampus: a mythological creature.  The hippocampus was part dolphin, part horse.  Archaeologists have found paintings to the hippocampus in the ruins of Pompeii. 

Hippocampus may also refer to a genus of fish with a neck and head that look remarkably like a horse.  We call them seahorses.  Evidently seahorses like being called seahorses.  They have never said otherwise.

The hippocampus is also the name of a section of your brain.  It is the section that regulates emotion. Scientists thought about calling this part of our brain the “seahorse.”  Humans, they guessed, would not be as compliant as the seahorse.  Therefore, instead of the clear, concise old Anglo Saxon, seahorse, the scientists went with the Greek “hippocampus.”  Which means seahorse.  Sort of.

Finally, the hippocampus, in modern slang, is (I did not make this up.  Do not get mad at me), a college campus containing a high ratio of obese students. 

Hippocampus comes from two Greek words.  ἵππος (hippos) means, horse.  Kάμπος (kampos) means, sea monster.