A line at the side of something.

Something that is additional or extra or that exists around the edges or margins of a main item.

A line for hobbling an animal by connecting the fore and the hind feet of the same side.

(sports) A line defining the side boundary of a playing field. Used in Canadian football, field lacrosse and basketball.

(sports) Usually in the plural: the area outside the playing field beyond each sideline.

(figurative) The outside or perimeter of any activity.

(Canada) A secondary road, especially a byroad at right angles to a main road.

(sports, transitive) To place on the sidelines; to bench or to keep someone out of play.

(figurative, transitive) To remove or keep out of circulation or out of the focus.