Affinity
An affinity is a bonus to skillgain in a given skill.
Each player developes one affinity in a random skill or characteristic after one month real time if he doesn't have at least one.
Additional affinities may be gained by killing other players in combat, provided the opponent is premium, has an affinity, and is of an enemy kingdom. It is possible to gain up to five affinities in each skill this way.
Skills for which you have an affinity can be seen by an asterisk symbol (*) next to their name in the skills window. Note that if you haven't unlocked that particular skill yet, it won't show up even if you have an affinity for it.
The effect on experience gain is 10% per affinity, stacking up to 5 times. It would be reasonable to assume that the maximum possible skillgain accrued from affinities (at the maximum stack) would be in the range of 50%.
An affinity in Fighting does not seem to have any effect.