sideline

UK: /ˈsaɪdlaɪn/ US: /ˈsaɪdˌlaɪn/ ,(sīd′līn′)

Inflections of 'sideline' (v): (⇒ conjugate)

sidelines

v 3rd person singular

sidelining

v pres p

sidelined

v past

sidelined

v past p

WordReference Random House Learner's Dictionary of American English © 2026

side•line /ˈsaɪdˌlaɪn/   n., v., -lined, -lin•ing. 
n. [countable]

1. an activity done in addition to one's regular job.
2. Sport
   • either of the two lines that make the side boundaries of an athletic field or court.
   • sidelines, [plural* the + ~;
     usually: on/from + the + ~] the place or circumstance in which one does not participate but simply observes:
     The former president could only watch from the sidelines while the new president took over the government.

v. [~ + object]

3. to remove from action:
   The pitcher was sidelined with an arm injury.

See -lin-.

WordReference Random House Unabridged Dictionary of American English © 2026

side•line  (sīd′līn′), n., v., -lined, -lin•ing. 
n. 

1. a line at the side of something.
2. a business or activity pursued in addition to one's primary business;
   a second occupation.
3. an additional or auxiliary line of goods:
   a grocery store with a sideline of household furnishings.
4. Sport
   • either of the two lines defining the side boundaries of a field or court.
   • sidelines, the area immediately beyond either sideline, where the substitute players sit.

v.t. 

5. to render incapable of participation, esp. in anything involving vigorous, physical action, as a sport:
   An injury to his throwing arm sidelined the quarterback for two weeks.

• side¹ + line¹ 1685–95, American.

Collins Concise English Dictionary © HarperCollins Publishers::

sideline / ˈsaɪdˌlaɪn/ noun

1. a line that marks the side boundary of a playing area
2. a subsidiary interest or source of income
3. an auxiliary business activity or line of merchandise

verb (transitive)

1. to prevent (a player) from taking part in a game