What is the planet that did not derived its name from a Greek God?

Well, technically...

Only one of the planets derives its name from a Greek god. The rest (except for Earth) are named after Roman gods. If they were named after Greek gods, they'd be Hermes, Aphrodite, (Earth), Ares, Zeus, Chronos, Ouranos, and Poseidon.

Ouranous/Uranus' Roman equivalent was Caelus.