I also had worked on a "horror universe" in the vein of The Cthulhu Mythos at one point, too, but kind of let it slide. Still it could come up here.
The Cthulhu Mythos is an interesting example of worldbuilding, though. H. P. Lovecraft did not set out with a definitely plan. He just wanted to have a sense of something bigger behind his stories so started dropping names and odd references to fictitious books and places. The locations, like Arkham and Innsmouth, were mostly drawn from his life. Arkham is mostly Providence and Salem, for instance. The names were sometimes made up (e.g. Cthulhu, Shub-Niggurath), sometimes borrowed from older works (e.g. Hastur). Most importantly, though, he left it as an open-ended shared universe. Friends and fellow writers like Robert E. Howard, Clark Ashton Smith, Henry Kuttner, and Robert Bloch used Lovecraft's elements in their stories and Lovecraft in turn borrowed elements that they added for his stories. In one memorable exchange, Lovecraft gave Bloch permission to kill him off in one of his stories (Bloch's first published story, IIRC) and then killed Bloch, under the alias Robert Blake, off in The Haunter of the Dark. Bloch wrote a further followup but IIRC, it did not come out until after Lovecraft's death put an end to the game. Basically, it was ad hoc worldbuilding and each writer kind of had their own take on it.
And so it continued, with various writers like August Derleth, Lin Carter, Ramsey Campbell, Brian Lumley, and even Stephen King borrowing from and adding to the Mythos. Derleth did try to codify it for a time, but that just made it less interesting and later writers tried to move away from Derleth's ideas.
Of course, it is pretty much the opposite of the worldbuilding in fantasy, which is often quite rigorous and carefully developed. Look at all the publications the Tolkien estate has got out of just compiling all J. R. R.'s notes and unused bits regarding Middle Earth. And George Martin has clearly put in a fair bit of time on A Song of Ice and Fire.
T. S. Eliot once wrote, "The naming of cats is a difficult matter. It isn't just one of your holiday games."
World building, especially in fantasy and s-f, can be like that. Unless you're a linguist like J.R.R. Tolkien (who knew and studied a number of Nordic and Germanic languages in his academic life), coming with names that sound like they belong together without have a whole made-up language to work with can be a big job.
I have been trying to keep the made-up names for my fantasy world kind of organized without going to the effort of making up whole languages. I am kind of going for a Hellenic sound for some, but others have gone more Germanic or English.
The name of the town in Night of the Wind, for instance, began as "Eversham", aiming for a rural English feel. Except I then named the fictitious city in my real world fiction "Eversham" as well and decided it fit better there. So I needed a new name. Having "gor" and "gar" as city name ending already, I decided that must mean "community" in the Tymuri languages (Tymur is the Northern continent of my world, kind of a mash-up of Europe and North America geographically). Madrygor has long been a major city in my imagined world, for instance. So, I came up with Avenigar. Does that mean something? Probably. Nethandra knows what though.
And I have no idea how or when I came up with the name Nethandra. It is the name of both the chief deity, a mother goddess, and the world in these stories. It has been in my head for so long, I really don't know the origins anymore. However, I have wrestled since with naming other deities, originally thinking they should all end in "dra" or similar. And I am still thinking that her consort, the sun god, will have a name along those lines though I haven't named him in a story yet. But I strayed for other deities I have used in stories, such as Denytha (the moon goddess and the patron of magic) and Talala (the "Dancing Goddess", patron of the arts and the city of Tantovar) so that convention is out the window now.
I could go on. I am even no longer entirely happy with the name of my protagonist, "Dev Jackalbury". It was was conceived when I had Avenigar as "Eversham" and meant to sound vaguely, but not quite, English. Does not quite fit that anymore, though, but I will live with it and sort it out sometime. He's not from Avenigar anyhow, but grew up further North, which I haven't really detailed beyond it being a rough, rugged region where a lot of their mineral resources are mined.
Enough for now. Any thoughts on naming things and using "made-up" words and languages? Ideas on how to keep the words feeling "real" without making up an entire language?
Starting a new story in my world, a sequel of sorts to Night of the Wind. Already realizing that magic is going to be a much bigger in this world than I had thought at one time. Niomi, the witch in the story, is moving into serious D&D wizard territory just in the first paragraphs. And I am not sure if I like that. Might cut back on it, though it also helps keep the timeline reasonable.
And that's a big thing with fantasy. Deciding how magical the world and the story is going to be, then being consistent in how it is used and the power level involved, is a big part of making the world more believable (in the sense of allowing a reader to suspend disbelief without being jarred loose by weird inconsistencies).
S-F can have the same problem. Star Trek frequently got itself out of jams using "technobabble" and then conveniently forgot it again, or presented a contradictory solution, in a future episode where it might have affected the plot. If a technology is stated to have x limitation in episode 10 and then does something that violates that limitation in episode 23, that's quite the same as a magic power being stated to have x limitation...
So, need to meditate a bit on how to handle the magic. Otherwise, I quite like what I have worked out for this story. Even has a vampire of a sort in it, one of my favorite fantasy-horror nasties (sorry, not a fan of sparkly loverboy vamps).