adj. Determined by chance, whim, or impulse, and not by necessity, reason, or principle: stopped at the first motel we passed, an arbitrary choice. adj. Based on or subject to individual judgment or preference: The diet imposes overall calorie limits, but daily menus are arbitrary. adj. Established by a court or judge rather than by a specific law or statute: an arbitrary penalty. adj. Not limited by law; despotic: the arbitrary rule of a dictator.