/ˈsaɪdlaɪn ||; ˈsaɪdˌlaɪn/noun1 [C] something that you do in addition to your regular job, especially to earn extra money 兼职，副业（尤指为了多挣钱）: He's an engineer, but he repairs cars as a sideline. 他是工程师，但兼职修理汽车。
2 sidelines [pl] the lines that mark the two long sides of the area used for playing sports such as football, tennis, etc; the area behind this （足球场、网球场等的）边线，界外区
on the sidelines not involved in an activity; not taking part in sth 当旁观者；当局外人