Ad arbitrium is originally a Latin phrase, which means according to one's discretion or option. It can be used to describe a situation where an individual has complete freedom or control over something. There are several synonyms that can be used to convey a similar meaning to ad arbitrium. These synonyms include at will, as desired, as one pleases, as one sees fit, at one's discretion, by choice, optionally, freely, voluntarily, etc. Each of these words allows the user to describe a situation where an individual has the power to do as they please. Whether it's choosing what they want to do or how they want to act, these synonyms emphasize the importance of having control over one's life.