luminary gold

 You can increase your chance to successfully hit an opponent in combat when you have increase agility levels. That is supported by the idea that in combat, opponents would not simply stand still allowing attacks to be dealt on each other. Think of fight scenes in films, although glorified, a certain amount of money would be used in melee combat to try to get around their guard and hit the opponent.
Increased thieving levels are supposed to increase as well as your chance to successfully dodge incoming attacks and be hit for zero damage. This doesn’t quite fit as well as agility but you can I imagine that being able to interpret your opponents strikes will allow you to block or dodge better.
The two skills would have the same effects as the attack and defense skills only on a much less dramatic scale, assembly at basically. I imagine if you could level these two skills and have a permanent attack and defense potion on your character (buy luminary gold).