When describing weapons and armour, it's pretty easy to fall into the boring trap of being generic. 

"He had a sword", "she had an axe", "she wore metal armour". 

Boring.

You can add a lot of life to your fantasy or historical writing by adding more specificity. Don't just describe someone as wearing 'armour', but talk about what kind of armour, what it looks like, what it feels like, how heavy is it? Is it cumbersome? Is it light and easy to move around in? What does it sound like when you smash it up with a sword?

And with weapons, a wider vocabulary will allow you to add more diverse imagery to your book. Maybe your hero has a flamberge instead of a generic two-handed sword, or a kopis instead of a shortsword! This could help them really stand out, not to mention the fact it's more interesting generally.

Equally, we can also use the way we describe weapons and armour to subtly add to our lore. Different shapes and styles will naturally come from different regions, built for different reasons. When you're writing your weapons and armour, try not to just think about what, but also why. Why does a character have that particular sword? What does it tell us about where they come from, or their life story? Why do the soldiers wear that outfit, or those colours?

Remember, when we show/don't tell we're not just describing things with better detail, we're also looking for opportunities to subtly tell stories. What someone wears tells a story of their life, or the lore of your world. Don't waste the opportunity!

When not to be specific

When showing weapons/armour and describing different styles, you need to keep in mind your audience. Will they know what a bevor is? Or a vambrace? Will they understand what a cuirass is versus a more generic term like breast or chest plate?

As you write, you'll need to think about how deep you can dive into specific terms without turning off your readers. 

If you're confident they'll know the terms, you're free to use what you like.

Not so sure? Perhaps use the terms you want to use, but describe them in detail at the same time so people know what you actually mean. 

Think they won't know any of it? Perhaps rename some of the pieces to generic alternatives. You can still show them and show how they work, you just might not drop "faulds" into your book as a specific word.

LISTS OF ARMOUR AND WEAPON TERMS

ARMOUR

(from Wikipedia List of medieval armour components)

(from World Anvil's article on Equipment - Armour)

(from EN World's thread Accessorising Your Fantasy Warrior: Shields, Gauntlets, & Helms)

WEAPONS

(from DeviantArt Japanese Weaponry by Kobra-Kan)

(from DeviantArt Medieval Weapons v.II by 6WingDragon)

(Artist unknown - can't find original source for this one)

(from Wikipedia entry on Swords)