Just using the term as a one off line would probably be De Minimis, though I’m not a Intellectual Property Rights attorney, so take this with a grain of salt or twenty.
There’s three parts to Intellectual Property Law; copyright, trademark, and patent. Copyright is the intellectual property law that protects what you
create artistically. “I wrote/painted/created this piece of art, it is mine.” Trakemark protects what you sell, at market. “I’m selling this product, you don’t get to sell your own product while pretending to be me.” Patent is the protection of inventions and innovation. “I made this thing, it does something unique, it’s mine, you can’t take my work and leave me with nothing.” None of these work exactly that smoothly, but it’s worth keeping in mind.
Incidentally, censoring out a random vowel does nothing, legally. If you’re going to say “Skyrim,” then just say it. There’s two ways this can go, copyright or trademark.
It’s worth pointing out that, yes, you can be sued, even without naming your setting. Fair use is an “affirmative defense.” This is the legal equivalent of saying, “yes, I did what they’re accusing me of, but the law they’re using don’t apply because of this.”
In copyright, Fair Use is usually examined through four (five) tests. Is the work transformative? What is the nature of the original work? How much did you take? What effect does the alleged infringement on the market for the original work? And, sometimes, what is “the character” of your use?
The transformative test is basically asking if you’re simply lifting copyrighted material wholesale. For a work to be transformative, it needs to alter the copyrighted material in some way fundamentally alter the nature or context of it. The best example of this are reviews and critique, which will take a copyrighted work, and then discuss it in detail.
Historically, simply lifting characters or settings, and using them in your own material, without substantially reworking them is not transformative, and as a result is copyright infringement. So, if you land your character in The Land of Skyr!m, and do nothing to differentiate it from the Tamerilic province, that’s going to be infringement. If you have a vaguely viking themed setting, and your character from the outside world wanders in, looks at the architecture, mountains, or whatever, and says it “reminds them of Eastmarch in Skyrim,” that’s probably not going to be infringing.
The nature of the original work is tested to determine if there’s a compelling interest to protect it. This one’s actually fairly complex, but what it basically means is that copyright law is more protective of art than non-fiction.
The amount of the work taken tests to see, exactly that. Did you simply copy down the bulk of the copyrighted work. This gets a little more complex in that you can potentially take “the heart” of the work, in a fairly concise excerpt, and actually commit copyright infringement.
Amusingly enough, if Pride and Prejudice wasn’t in the public domain (meaning the copyright has expired) Pride and Prejudice and Zombies would be an excellent example of a situation where the work passes the transformative test, but completely fails the substantiality test, because it copies the entire text. Similarly, if I’m remembering correctly, most annotated texts face the same issue, even though they substantially expand the work’s context.
The effect of your work on the copyrighted work’s market is tested to determine if you’re actually harming the copyright. Either by not licensing the work, or by offering an alternative to the copyrighted work. If you’re playing a song at a commercial venue without paying the rightsholders, that’s infringement, because it should have been licensed, even if you’re not making money off of it. In cases where you’re providing an alternative to the original material, that’s still potentially infringing. The example above would be annotated works, where they function as an effective alternate option to reading the original material. A heavily cut down version of the text could also function as an alternative.
The example that comes to mind are film remixes, where an entire film is condensed into 10 to 15 minutes without fundamentally loosing the substance of the film. This is slightly different from taking the heart of the work, which, in theory, can be achieved by taking a single line or scene.
The final test, is the character of use, this is examining what you’re doing, in a larger sense. If you’re using excerpts of copyrighted material for educational purposes, then it is less likely you’ll be found infringing. Similarly, if you’re engaging in non-commercial use, such as fanfiction, then this is the test where it applies. It’s worth stressing, simply engaging in non-commercial use, does not automatically exempt you from copyright infringement.
So, that’s copyright. Simply using the name Skyrim, and saying, “yeah, this reminds me of Skyrim,” without actually attempting to copy or emulate the setting should be fine. Just like you can have character say they enjoyed watching Star Wars, or Star Trek. You can also, certainly, have characters talking about about copyrighted settings without an issue. The thing you can’t do is actually use those settings for your own work. (Again, remembering that fanfiction exists in a sort of legal limbo. Without a prior agreement from the rightsholders, it is technically infringement, but there’s no value to be had from litigating. Though that’s never stopped the Tolkien Estate from going after everyone that looked at them funny.)
Trademark also has its own fair use defense, and it operates under completely different rules. Again, it’s an affirmative defense, so it only comes into play after you’ve been sued, but it’s the same basic idea, “I did something that looks like infringement, but it’s not.” Also, fair warning, I’m a lot less versed in trademark law, so there’s probably going to be some errors here.
As mentioned above, Trademark law is primarily concerned with ensuring that brand confusion does not occur between two products. Fair use usually operates off the idea that you did use another company’s trademark, for the purposes of referencing their mark specifically.
That means you can’t sell products under that name, and you can’t claim to be endorsed by the trademark. You can still say something reminds your character of Skyrim, just like you can say they wanted McDonalds, a Coke, or any number of other consumer products. That’s not what Trademark is designed to prevent. What you can’t do is sell your book as Skyrim, or even as “a Skyrim story.” Not that it matters, but the part where you also wouldn’t be using the font from Skyrim’s logo is actually relevant to trademark fair use.
I’m actually conflating normative and traditional fair use in Trademark law. Strictly speaking, normative fair use is when you reference someone else’s mark, while traditional fair use is when you’re referencing your own product, and it could be mistaken for the registered trademark. So the tests are slightly different between these two situations.
Again, if you’re just having a character say that the world they’ve found themselves in reminds them of Skryim, that would be normative fair use. If you were trying to market your book under the name Skyrim, or the “a Skyrim story” mentioned above, then that would be traditional trademark infringement.