Okay, so this actually started a lovely debate between a few friends of mine, and there isn't quite a good answer.

If you look at Latin derived languages such as French, Spanish, and Italian, they are all derived from the latin word "Terra" which of course has the association with the goddess Terra or Gaia, which was a "Primeval God", or one of the elemental Gods that existed before the main Pantheons that included ones like Jupiter, Mars, Venus, etc.

However, you have to remember that English is not a Latin language, it's Germanic in it's roots.

If you refer to this table, you'll see that in most European languages, the names for the planets follow a Greco-Roman mythological naming scheme that has been adapted into their language.

But the Earth itself? Not so much. Germanic, Romantic, Balto-Slavic, all seem to have different names for the Earth, and this is where it get's tricky.

English itself is a language that derives from Germanic and Latin sources due to the intermingling of the Anglo-Saxons (Germanic) and Normans (French/Romantic). Some words in modern English do derive from Anglo-Saxon while others come from the Norman influence, while some derive from Nordic influences as well.

So, what does that mean? Well, with an unfortunate lack of written records, a jumble of cultural inheritances, and lost origins...we frankly are guessing at the origin of the word "Earth" as it is presented in the language. We do know that "Earth" is derived from the Old English word "eorþe" which is defined as:

"ground, soil, dirt, dry land; country, district," also used (along with middangeard) for "the (material) world, the abode of man" (as opposed to the heavens or the underworld)

The problem here is, beyond that, we don't know where the word comes from and if it is associated with a Germanic god or goddess, or is simply a word that describes the ground we walk on or the world we live in. The word "Earth" has been used to describe the planet we inhabit since about the 14th Century and has stuck in our language since then.