There are 3 item properties: protections, resistances and purposed vs. (versus)Protections are versus: fighter, mage priest, thief, midget, giant, mythical, dragon, animal, were, undead, demon, insect, enchanted. I don't know how this works, I would have to test with an editor, but searching in my memory some 23 years back and that is if I remember correction, I never got hit by monsters for which I had protection against, then again this remains to be double-checked.
Resistances are versus: no elements (don't know what this one means except my guess is it protects agains spells such as Molito), fire, cold, poison, leveldrain, stoning, magic (don't know which spells this protects from). How this works is if an item has one of these properties it just means your character wearing the item will be imprevious to one (or many) of these types of monsters attacks.
Purposed versus are: fighter, mage priest, thief, midget, giant, mythical, dragon, animal, were, undead, demon, insect, enchanted. This just means you will be doing double damage with your attack, just like when a monster is asleep you are doing double damage... now if a monster is asleep and you have such a weapon will you be doing 4x damage? I don't know, i have never tried.
Snafaru