Merriam-Webster Collegiate Dictionary - hippocampus

 noun  (plural hippocampi)  Etymology: New Latin, from Greek hippokampos sea horse, from hippos horse + kampos sea monster — more at equine  Date: 1706 a curved elongated ridge that extends over the floor of the descending horn of each lateral ventricle of the brain, that consists of gray matter covered on the ventricular surface with white matter, and that is involved in forming, storing, and processing memory  • hippocampal adjective