Arbitrary

From Middle English arbitrarie, Latin arbitrarius ("arbitrary, uncertain"), from arbiter ("witness, on-looker, listener, judge, overseer")

(usually of a decision) Based on individual discretion or judgment; not based on any objective distinction, perhaps even made at random.Benjamin Franklin's designation of "positive" and "negative" to different charges was arbitrary. In fact, electrons flow in the opposite direction to conventional current.The decision to use 18 years as the legal age of adulthood was arbitrary, as both age 17 and 19 were reasonable alternatives.
Determined by impulse rather than reason; heavy-handed."The Russian trials were Stalin's purges, with which he attempted to consolidate his power. Like most people in the West, I believed these show trials to be the arbitrary acts of a cruel dictator." (Max Born, Letters to Einstein)
(mathematics) Any and all possible.The equation is true for an arbitrary value of x.
Determined by independent arbiter.To secure food safety, there should first be a national standard to arbitrarily state what is wholesome and what is not; second, the final buyer should know exactly what he is purchasing. (The World's Work ...: a history of our time)

Full definition of arbitrary