Arming Sword

The original dueling sword, the arming sword has a generally triangular profile and rhombus/diamond cross-section, and a tapered tip, lending it great strength relative to its weight, and a very low center of balance, near the hilt. It can be paired with an off-hand blade, used with great force without fear of breaking, swiftly repositioned around its center of balance, or gripped hand-and-a-half style for added power and control. The range of options in its use made it quite popular well into the lifespan of other smaller dueling swords made after it.

Additional Weapon Properties. 

Parry. If a creature hits you with a melee attack while you are wielding a weapon with the parry property that you are proficient with, you can use your reaction to add half your proficiency bonus to your AC for that attack, potentially causing it to miss. If you are wielding two weapons with the parry property, you add your entire proficiency bonus instead, so long as you have proficiency with both items.

Skewering. These precise weapons reward focused attacks and punch holes in enemy defenses. When an attack roll with a skewering weapon exceeds the target's AC by 5 or more (or lands a critical hit), the next attack made against the target gains a bonus equal to your proficiency bonus.

Slicing. These wicked weapons cut gaping wounds into the flesh, causing profuse bleeding. When an attack roll with a slicing weapon exceeds the target's AC by 5 or more (or lands a critical hit), the target takes additional necrotic damage equal to your proficiency bonus. Constructs, elementals, most undead, and other targets that do not bleed may be immune to this damage at the discretion of your DM.

Proficiency with a Longsword allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Ignore Weapon Property: Versatile, Damage, Combat, Versatile, Sap