Sharp = better at piercing enemy armor
Slim (old name for slender or willowy?) = weighs less
Durable (old name for sturdy?) = can't be destroyed while you're carrying it
Flaming = if you plug a battery in it, it'll deal some fire damage that ignores enemy armor in addition to its normal damage, but also slowly drain the battery
Electricity = same as flaming, but with electric damage that can also arc across multiple creatures if they're next to each other

If you put the pointer next to an item in your inventory and click the tab key, you'll get a description of the item. If an item has any of these modifiers, the description should give some explanation of what the mod does.