Definitions
1.nounA line at the side of something.
2.nounSomething 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."
3.nounA line for hobbling an animal by connecting the fore and the hind feet of the same side.
4.nounA line defining the side boundary of a playing field.
5.nounUsually in the plural: the area outside the playing field beyond each sideline."The coach stood on the sidelines and bellowed commands at the team."
6.nounThe outside or perimeter of any activity."She installed the whole fixture while he simply watched from the sidelines."
7.nounA secondary road, especially a byroad at right angles to a main road.
8.verbTo place on the sidelines; to bench or to keep someone out of play."The coach sidelined the player until he regained his strength."
9.verbTo remove or keep out of circulation or out of the focus."The illness sidelined him for weeks."