If you are referring to the planet Neptune, than i'd say it was derived from the name of the Roman god Neptune, the god of the Oceans as well as earthquakes.
If you are speaking of the actual word Neptune, than i am afraid i can't help you out.
Triton
The Neptunes
The Neptunes was created in 1990.
The Spongebob Movie game
neptunes gravity is high
Hercules is the Roman name for the Greek divine hero Heracles
Neptune is Poseidon's Latin name. His siblings are Hestia, Demeter, Hera, Zeus, and Hates.
There are a couple of listed nicknames for the planet Neptune. These include the Blue Planet and the Great Gas Giant.
hydrogen and helium
It was discovered in 1846.
gas
Hera & Zeus