- 1[countable] an activity that you do as well as your main job in order to earn extra money His hobby of winemaking was fast becoming a profitable sideline.
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- 2sidelines [plural] the lines along the two long sides of a sports field, tennis court, etc. that mark the outer edges; the area just outside these The coach stood on the sidelines yelling instructions to the players. Idioms
watching something but not actually involved in it He was content to watch from the sidelines as his wife built up a successful business empire. She has chosen to remain on the sidelines of public debate.
Check pronunciation: sideline