- a line at the side of something.
- a business or activity pursued in addition to one's primary business; a second occupation.
- an additional or auxiliary line of goods: a grocery store with a sideline of household furnishings.
- Sports.
- either of the two lines defining the side boundaries of a field or court.
- the area immediately beyond either sideline, where the substitute players sit.
- the position or point of view taken by a person who observes an activity or situation but does not directly participate in it.
- to render incapable of participation, especially in anything involving vigorous, physical action, as a sport: An injury to his throwing arm sidelined the quarterback for two weeks.
- a line that marks the side boundary of a playing area
- a subsidiary interest or source of income
- an auxiliary business activity or line of merchandise
- to prevent (a player) from taking part in a game
- to prevent (a person) from pursuing a particular activity, operation, career, etc
