"He comes towards me, the wavy blade of his flamberge moving, snakelike, in the flickering torchlight."

Flamberge does not automatically mean a sword is wavy.

That's the origin of the term, but it has been used for a long time to refer to many swords, some of which are not flame or wave-bladed.

I think you should explain it once and then leave it at that. Expect the reader to remember what it is the next time the word appears. And if it's a series of books once per book.

The character wouldnt say it. It knows the sword. But the narrator should use jargon. People need to be educated about new words

Thank you for that, honestly I just used the term that sounded fanciest.

Of course, some creativity is to be had with it. I couldn't have done a better job of naturally and clearly explaining the term.

I agree. People know too little of swords. My problem is easier to solve when you're writing in a third person like you point out.

Thank you!

If the character is a teacher it makes sense the way you wrote it, if not ot just feels like unrealistic conversation

I would avoid jargon all together unless it actually adds something. Even then I would go with the first option.

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'I would that I could draw back but found to my despair, and shamed though I was it to my secretest delight, that I was as firmly transfixed by the quivering of his sturdy flamberge as banquet goat is fixed on a spit. Reader, I fucked him.'

Sorry. '. . . goat is fixed on a spit. "I have heard tell of your undefeated flanchion," I sighed defiantly, "but perhaps your flamberge excels it." '

Delightful. What's a flanchion?

Thanks, but it's you deserves all the credit. (Though I must say I'm rather pleased with 'sighed defiantly'.)

I can tell you exactly what a flanchion is. It's a word on a wiki list of medieval swords.