A physical pillar or support that holds up a structure; figuratively, a mainstay or key support (person/element) of an organization or system.
この橋は古い木製の支柱で支えられている。
This bridge is supported by old wooden piers.
彼はチームの支柱として、プロジェクトを牽引した。
He led the project as the team's mainstay.
工事中は仮の支柱を立てて壁を補強した。
During the construction work they put up temporary supports to reinforce the wall.