Earth is the only planet in our solar system that is not named after a god
The planet names have derived from Roman and Greek mythology, except for the name Earth which is Germanic and Old English in origin. The five planets easily visible with the unaided eye (Mercury, Venus, Mars, Jupiter, and Saturn) have been observed for all human history as far as we can tell, and they were called different things by different cultures. These Roman names were adopted by European languages and culture and became standard in science.
The Romans named these planets according to their movements and appearence. For example, Venus, the planet that appears the brightest, was named after the Roman goddess of beauty, while the reddish Mars was named after the god of war.
Venus - Roman goddess of love, beauty, sex, seduction and fertility.
Mars - Roman god of war and also an agricultural guardian.
Mercury - messenger and a Roman god of trade.
Jupiter - Roman king of the gods, and the god of the sky and thunder
Saturn - Roman god of agriculture, justice and strength.
Uranus - primal Greek god personifying the sky.
Neptune - Roman god of water and the sea.
The name "Earth" derives from the Anglo-Saxon word erda, which means ground or soil, and is related to the German word Erde. It became eorthe later, and then erthe in Middle English. The standard astronomical symbol of the Earth consists of a cross circumscribed by a circle.