Your book's universe is not ours. There is allowed to be a dissonance between how things work in your world, and how they work in ours. There's allowed to be different definitions to words in your world, and ours. This effect is especially strengthened by the fact that your book is within the Fantasy genre.

So if you're able to establish what pyromagus with clarity, then the reader will accept it. You'd be surprised to know how much readers will accept, as long as they understand it (to the extent they're supposed to).

To give an example. I am reviewing someone's book, and in it, the word telepathy is used to describe an ability a species has. This ability has a large scope. Not only can they, without words, communicate thoughts, memories, feelings, associations, impressions, etc., but they can take over each others bodies, to some extent.

Now, the taking over of someone's body is not within the definition of telepathy (at least that I know of, which is what's relevant). Doing something like that is more akin to psychokinesis or astral projection. Yet, when I found out this ability was apart of the universes' definition of telepathy, I was only excited and pleasantly surprised upon the ability's utilization. This is the power of dictating how your fictional world works. You can twist and subvert so much, to a great effect.

Your book's universe is not ours. There is allowed to be a dissonance between how things work in your world, and how they work in ours. There's allowed to be different definitions to words in your world, and ours. This effect is especially strengthened by the fact that your book is within the Fantasy genre.

So if you're able to establish what pyromagus means, with clarity, then the reader will accept it. You'd be surprised to know how much readers will accept, as long as they understand it (to the extent they're supposed to).

To give an example. I am reviewing someone's book, and in it, the word telepathy is used to describe an ability a species has. This ability has a large scope within his world. Not only can they, without words, communicate thoughts, memories, feelings, associations, impressions, etc., but they can take over each others bodies, to some extent.

Now, the taking over of someone's body is not within the definition of telepathy (at least that I know of, which is what's relevant). Doing something like that is more akin to psychokinesis or astral projection. Yet, when I found out this ability was a part of the universe's definition of telepathy, I was only excited and pleasantly surprised upon the ability's utilization. This is the power of dictating how your fictional world works. You can twist and subvert so much, to a great effect.