But the big one here is the characteristic word. By adding Fenyx Rising, it could be argued that that, in addition to the material differences between the products, there is enough separation to ensure there is no risk of confusion from audiences. There are also multiple Immortals trademarks which could make that word in and of itself less defensible depending on the potential conflict.

That’s basically it right there. The word “immortal” has multiple dictionary definitions tracing back long before any trademark, including a [prominent ancient military unit](https://en.wikipedia.org/wiki/Immortals_(Achaemenid_Empire\)) so any trademark around that word isn’t strong enough to prevent any use of the word as a normal word, or even as part of another trademark when used descriptively.

The strongest trademark protection comes for words that are totally made up for the purpose of the product or company. Something like Hulu or Kodak.

Next up are probably mashed up words that might relate to existing words but are distinct mashups or modifications, like GeForce or Craisins.

Next up, words that have meaning but are completely unrelated to the product itself, like Apple (computers) and Snickers (the candy bar) or Tide (the laundry detergent).

Next up are suggestive marks where the trademark relies on the meaning to convey something about the product itself, but still retains some distinctiveness: InSinkErator is a brand of in-sink disposal, Coffee Mate is a non-dairy creamer designed for mixing into coffee, Joy-Con is a controller designed to evoke joy, etc.

Some descriptive words don’t get trademark protection until they enter the public consciousness as a distinct indicator of its origin or manufacture. Name-based businesses often fall into this category, like a restaurant named after the owner, and don’t get protection until it’s popular enough (McDonald’s is the main example).

It can get complicated, but the basic principle underlying all of it is that if you choose a less unique word as the name of your trademark, you’ll get less protection against others using it.