What in the world should you call your world?
It’s all based on what you want to convey to your audience. Is this world named by you directly, as a wink to your readers? Maybe you’d want to give them a literal overview by describing the shape of it. Think Larry Niven’s Ringworld or Terry Pratchett’s Discworld. It’s a practical and cheeky option, especially if your globe isn’t an actual globe.
Or maybe you want to evoke a wider mythology. JRR Tolkien’s Middle Earth suggests a connection to Norse mythology. While Middle Earth is Midgard’s equivalent, both in name and in the fact that it’s Earth, the story doesn’t really sprawl into other worlds.
There’s no full Ygdrassil and Nine Realms. It’s all Middle Earth, but that doesn’t feel sparse because Tolkien stuffed it to the hilt with peoples and kingdoms and mythologies of its own. LotR’s epic setting is more than massive enough.
However, maybe a peek behind the curtain isn’t what you’re going for. Rather than directly telling your audience information about the world via its name, you’d prefer to keep it within the fourth wall and have your characters name their world. This is akin to having your characters named by their parents.
That means you’re confined by what the characters know about their world: what do they think it looks like and can they see beyond its boundaries? This means thinking about the technology, philosophy, and even religious beliefs of your characters. What do they believe about the shape of the world, their place in it, and the meaning of it all?
In real life, figures like Copernicus and Galileo fiercely rocked the boat by spotting evidence that the Earth isn’t the center of the solar system. Think about the kind of society that would be completely revolutionized by such a discovery. If you’re writing about a medieval society, do they even know that their planet is round? All of this information factors into how the people would think about the world, and therefore, what they’d call it.
Other things to consider are what your society values (nature names, references to historical leaders, names that evoke their pantheon, etc) and how your society uses language. In real life, many city names have suffixes like -ton, -ville, and -berg/-burg. If you’ve already established a generic name for a small town or village, perhaps that’s the suffix that gets tacked on. Then you get city names like Mapleblorp and Henrysquish and Dragon Springs. That is, build the concept for how places get named and then apply the formula.
Better yet, build multiple concepts to keep it fresh. This is especially important if you’re writing a world that’s a mix of diverse cultures. Each one of those cultures is going to have a handful of names and language traits that keep showing up in town names. Perhaps there are multiple names for the world as a whole.
And finally, consider if your characters even know about places beyond their immediate world. If they don’t, then maybe your world doesn’t need a specific name. It’s just what’s there.
If your setting is the characters’ entire universe, they don’t need a name for what’s beyond it because they don’t have that concept. Perhaps then, they don’t need names for places beyond their home and the neighboring kingdoms.
The bottom line is, the name of your world is a message to your audience. It’s how you tell them what your characters know of their surroundings and how they experience living there.