I love, love Brandon Sanderson but I feel like every time he needs a "magic word" he just takes two regular words and jams them together.
Dreamshard, Shardblade, Shardplate, Lightweaving, Mistborn, Coinshot, Pewterarm, Coppercloud, Surgebinder, Soulcaster, etc etc etc
Sorry u/Mistborn I still love you
It's done intentionally. Let's look at our options.
I can create all-out fantasy words for terms like this. (Lait or crem from Stormlight are examples.) Problem is, the more you do this, the more you pile a difficult linguistics on top of a reader. The more words like this they have to learn, the more difficult it is to get into a story. If you were doing it, perhaps you'd go this direction. I feel that overloading on these terms is dangerous. Already, the main reason new readers put down my books is that they feel overwhelmed by the worldbuilding.
So we have the second option. Use a latin, germatic, or greek root and create a word that FEELS right, has some mental connection for the reader, but which isn't a real word. Allomancy/Feruchemy/Hemalurgy. Veristitalian. To a lesser extent, Elantris.
This so called "Harry Potter Spells" method gives some familiarity to the naming, makes them stick a little better in people's heads, which makes the books a little easier to get into. But they're also distracting to some readers who say, "Wait. There's no Latin in this world, so where did Latin root words come from?" And for others (particularly in translation) those roots mean nothing, and so these all end up lumped into the first group.
The final method is the pure Germanic method--creating compound words. It works in English very well because of our Germanic roots--and is one of the main ways (other than turning nouns into verbs or the other direction) that we create new words. Supermarket. Masterpiece. Newspaper. Thunderstorm. Footprint. Firework. Heartbeat. Yourself. None of those look odd to you because they are words that are "meant" to go together in your head.
I use some of batch one, some of batch two, but I do favor batch three--it does what I want it to. Works in the language, has an "otherworld" feel but is also very quickly understood by someone new to the series. There are arguments for all three methods, however.
You can also just go the route of using an English word despite it clearly not being accurate.
"He tied a ribbon around his horse's third antennae, and patted its chitinous flank."
Agreed. Re-contextualizing English words can work too--I find it particularly useful to do what I mentioned above. Take a verb and make it a noun or vice versa. Or use a verb in a way that you normally don't. (Awakeners or Lashings are examples from my work, though Spice from Dune is one of the grand-daddy examples of this. As it is for a lot of fantastical linguistics.)