Being on refers to the state of being active or engaged in something. There are several synonyms that can be used interchangeably with this phrase in order to add variety and texture to written or spoken language. For example, the term 'in action' can be used as an alternative to being on, as can 'operational', 'functioning', or even 'in progress'. Another synonym for being on is 'up and running', which is often used to describe the state of a machine or system that is functioning correctly. Meanwhile, the term 'in motion' can be used to describe a person or object that is actively moving or engaged in an activity.