Physical or metaphorical support: a pole, strut, or person/thing that holds something up or serves as a mainstay.
We drove props into the ground to set up the tent.
He is the emotional pillar of the team.
I set up a support pole for the tomato seedling.
He became the mainstay of the team.
I secured the support pole in preparation for strong wind.
柱 is a general architectural pillar or column, while 支柱 is specifically a prop or brace added for support, often temporary or supplementary.
大黒柱 is used specifically for the person who is the main breadwinner or pillar of a family, whereas 支柱 can refer to any supporting pole or figure, physical or metaphorical.
支柱 is a general support post or prop (e.g. for plants or scaffolding), while 杭 specifically refers to a pointed stake or pile driven into the ground.
支柱 is a general term for a pillar or supporting post, while 突っ張り refers specifically to a temporary prop or brace wedged in to hold something rigid.
支柱 literally means a supporting pillar and is used for the central support of a plan or group, much like バックボーン in its metaphorical sense.
支柱 (shichū, "prop/post/pillar") is long and thin, so it's counted with 本 (hon).
prop word
Compound of 支 (support) and 柱 (pillar). The exact historical derivation is uncertain, but the kanji directly reflect the meaning of a supporting pillar or prop.