Auxiliary; supplementary: Now he has a side-bar job, hustling beer or sports equipment (1950s+)
noun[adjective and first noun senses probably fr the late 1800s use of sidebar buggy or wagon for a vehicle having longitudinal reinforcements along the sides; perhaps fr side-bar, ''an auxiliary toll-gate on a road leading into a main toll-road''; second noun sense fr auxiliary bars, legal or courtroom sites and barriers, formerly found in the Scottish and English parliaments, and so noted by 1708]