Definition of

Sideline

  1. (noun, act) an auxiliary activity
  2. (noun, artifact) an auxiliary line of merchandise
  3. (noun, location) a line that marks the side boundary of a playing field
  4. (verb, social) remove from the center of activity or attention; place into an inferior position

via WordNet, Princeton University

Origin of the word Sideline

  1. "lines marking the limits of playing area" (on a football field, etc.), 1862, from side (adj.) + line (q.v.). The fig. sense of "position removed from active participation" is attested from 1934 (because players who are not in the game stand along the sidelines). The verb meaning "put out of play" is from 1945. more

via Online Etymology Dictionary, ©2001 Douglas Harper

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