The words hippo and campus; literally a combination of horse and monster in ancient Greek. However, the hippocampus or hippocamp is also often called a sea-horse in English.
In Greek mythology, the Hippocampus was a mythological creature. It has typically been depicted as a horse in its fore-part with a coiling, scaly, fishlike hindquarters.
Homer describes Poseidon, who was god of horses, earthquakes, and the sea, drawn by brazen-hoofed horses over the sea’s surface. Apollonius of Rhodes on the other hand, being consciously archaic in Argonautica, describes the horse of Poseidon emerging from the sea and galloping away across the Libyan sands.
In Hellenistic and Roman imagery, however, Poseidon often drives a sea-chariot drawn by hippocampi. Thus hippocamps sport with this god in both ancient depictions and much more modern ones, such as in the waters of the 18th-century Trevi Fountain in Rome surveyed by Neptune from his niche above.