olemus
Wiktionary:
adj
1. (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.
The decision to use 18 years as the legal age of adulthood was arbitrary, as both age 17 and 19 were reasonable alternatives.
2. determined by impulse rather than reason; heavy-handed
(mathematics) Any, out of all that are possible.
3. the equation is true for an arbitrary value of x