arbitrary meaning , definition , what is arbitrary : decided or arranged without any reason o...: Learn more. The meaning of ARBITRARY is existing or coming about seemingly at random or by chance or as a capricious and unreasonable act of will. How to use arbitrary in a sentence. Arbitrary means based on chance or personal power, not reason or rules. Learn how to use this adjective in different contexts with synonyms, antonyms, and examples from the Cambridge Dictionary. ARBITRARY meaning : 1. based on chance rather than being planned or based on reason: 2. using unlimited personal power…. Learn more.