支柱 (zhīzhù) means both a literal structural pillar and a figurative mainstay or backbone of a group or system. Among HSK7 siblings, 栋梁 (dòngliáng) is a near-synonym but more literary, often used for a nation or organization's key figure; 脊梁 (jǐliáng) focuses on moral backbone or the literal spine. 支柱 is the most versatile and common term for both literal and figurative senses.