The antonyms for the term "left service" are "joined service", "enlisted", "enrolled", "enlisted in", and "signed up". These terms are used to describe the process whereby an individual begins working for or with an organization, company or institution. When a person joins a new job or signs up for a new service, they are not leaving their previous one, but instead are starting a new chapter in their professional life. By contrast, when someone leaves service, they are ending their employment or discharging from duty, usually due to a variety of reasons such as retirement, resignation, or termination. Choosing the right antonym will depend on the context of the sentence or conversation.