Definition from Wiktionary, the free dictionary
- A line at the side of something, as in "the yellow sideline of the road".
- (sports) A line defining the side boundary of a playing field.
- (usually in the plural) The area outside the playing field beyond each sideline.
- The coach stood on the sidelines and bellowed commands at the team.
- The outside or perimeter of any activity.
- She installed the whole fixture while he simply watched from the sidelines.
- Something that is additional or extra or that exists around the edges or margins of a main item.
- She started the business as a sideline to her regular work and it ended up becoming the greater source of income.
- Soup need not be just a sideline to a meal; if you like, it can be the main course.
sports: side boundary of a playing field
something additional or existing around the margins
- (transitive) To place on the sidelines; to bench or to keep someone out of play.
- The coach sidelined the player until he regained his strength.
- (transitive) To remove or keep out of circulation.
- The illness sidelined him for weeks.