Are arbiter and arbitration arbitrary?

A large portion of the words we use today come from Latin roots. Many of these words retain a meaning that is closely related to their Latin ancestor, although sometimes they will drift a considerable distance from their roots (sinister, for instance, had the meaning of “on the left side” in Latin, but also meant “unlucky, inauspicious”). In some instances, a single Latin word will give rise to multiple words in English, some of which have strayed in meaning, and others which have not.

An example of this may be found in our word arbiter. We trace it to the Latin root with the same spelling, arbiter, meaning “eyewitness, onlooker, person appointed to settle a dispute.” A number of English words stem from the Latin arbiter, many of which have to do with judging or being a judge. An arbiter is a judge, and arbitration is the act of judging, or serving as an arbiter. Yet the most common meaning of arbitrary is “existing or coming about seemingly at random or by chance or as a capricious and unreasonable act of will,” which seems to be quite a bit different in meaning from the other two words. Arbitrary does indeed come from the same Latin root, and its oldest meaning in English was “depending on choice or discretion particularly regarding the decision of a judge or a tribunal.” But over time it developed additional senses that are somewhat removed from that initial meaning.