He himself stated (foreword to The Hobbit) that “dwarfs” and “dwarfish” were the correct English plural and adjective, and in his writing he used “dwarves” and “dwarvish” only to refer to Durin’s Folk - so “dwarfs” would be small people who were not Naugrim or Khazad if you prefer. And since Pterry, to name but one, intended his dwarfs to be clearly distinguished from those of Middle-Earth - as are Narnian dwarfs - he (and Lewis) used the normal English plural. But “elfs” is not a pluralisation I have ever encountered before.
My pah-swaydo dragon and I would like for you to withdraw the question, good sir!
I know a puh-lad-in who would agree. 
(Not my personal mispronunciation, mind you…I joined a D&D group as an adult, after playing for many years with other groups, and found that the entire group pronounced “paladin” in that way. I thought it was an in-joke at first, but later learned that they all simply thought that was the pronunciation.)
That sounds like a highly improbe-able kircumstance.
Most of the words in this thread I first encountered elsewhere, but there’s a specific category of magic that I hadn’t – geas, grimoire, lich, elemental sand other such “technical” terms I first encountered reading fantasy fiction.
There are a several obsolete words I first encountered in fantasy fiction – drinking jack, prie-dieux, groat (meaning an old type of coin).
Fa-kay-de (façade) comes to mind.
If we don’t all pronounce things the same, CHA-ows will ensue. Hypothetically. Chaos may also be a problem.
Oh, here’s a good one. Back in the day, I was reading the treasure charts for monsters in D&D (or AD&D) and came across “nil”. I somehow decided that “nil” was a material, kind of silvery and malleable. Maybe I got the idea from “nickel” or something… God only knows.
But for a good while, characters going through adventures I created were often rewarded for their efforts with great bags of nil.
They talk about Runes in the Harry Potter books which, while still in the fantasy/sorcery category, is much more mainstream.
And I’m baffled that your father is unfamiliar with the word familiar – if not the witchy definition, then at least the more common one? Am I missing something? Have I been misspelling familiar all these years?
In your defense, the Latin circum is pronounced kir kum.
Oh wait, that’s my defense. This actually came up just last week (not circumstance) but with a different word with a Latin root that I mispronounced with a hard C. I can’t remember the word right now, but I do remember stating that it’s from Latin anyway. 
Coup de grace, in Poli Sci. Hey, I’m in the province where bilingualism means English and Cree, not English and French, gimme a break.
‘Drow’ is another fantasy term. Interestingly enough, I’ve never run into a fantasy anime that was localized into English and used the word, which makes me think of copyfight issues.
I think “drow” is D&D-specific.
I don’t suppose “amulet” is in particularly common usage these days.
Or “weregild.”
you’d be surprised the number of people who couldn’t tell you the differences between a mace, morning star, and a flail.
Of course, the ones who can tell you the difference are the same ones who will spend hours arguing about which is which.
Though Gygax created the concept of drow as dark elves, the word seems to have its roots in Scottish dialects, where “trow” (or “drow”) was used for evil sprites.
Much like life itself, really. Certainly I’ve known HR departments who took exactly that approach, even if they were smart enough to try and hide it.
Philter
Unguent
I recall an article where Isaac Asimov mentioned having that happen to him with “Betelgeuse”, complete with him “correcting” people who used the right pronunciation.
Another thing I got from Tolkien was the difference between “fay” and “fey”.
fay = noun, meaning “fairy”
fey = adjective, meaning “knowing that you are fated to die soon, and being cool with it”
Ha ha ha, I had the exact same experience.
I also learned “tome” from Dungeons and Dragons, and I had to explain what that word meant to my Grade 7 teacher when I used it in a story.