The Armorial Art revolves around gracefully strapping large chunks of metal to your body.
Thick SkinYou like getting hit, it builds character! Increases your life-force and chance to block attacks.
Suit UpTo be armoured you must project the image of being armoured. This skill allows you to tighten the straps on your armour so that you use it more effectively, but this bonus is lost if you get hit too much.
It Only Makes You StrongerPractice being beaten, crushed and stabbed has made you highly skilled in these activities. When you get hit there is a chance that your health, burliness, and piercing resistance will increase temporarily.
Master of Arms doesn't require any particular armour to be worn to gain any of these benefits (even though it feels like its geared towards heavier armour), so even a wizard build can take this and be more defensive.
Due to Suit Up's bonus to regeneration, trying to have it on at all times is recommended. Since it has a cooldown of 40 turns, its good to click this on after a hard fight to make healing a little faster.
Thick skin is currently bugged. It's supposed to provide +3 +5. (Note: by 2015, the skill reports the information at the top and provides it. This "bug" is now only a bug if the phrase "supposed to provide" reflects the developer's intention.)