Armor Cleaving
From Drunkapedia
Armor Cleaving gives the item the ability to ignore some of its opponent's armor. Unlike Armor Rending, the amount of armor it ignores is fixed. Because this reduces by a percentage, it is most effective on creatures with very high armor, it is less effective (not as much of an increase in over other options) when the natural armor is either low, or has be reduced a lot by the life magic vuln Imperil.
This property is only found on quest weapons.