1. the fundamental basis or foundation that supports something
Usage: often used metaphorically
2. structural supports placed beneath a building or wall
Usage: construction/architecture

Examples

• The theoretical underpinnings of the research were solid.
• We need to examine the moral underpinnings of this decision.
• The economic underpinnings of the policy remain unclear.
• Engineers reinforced the building’s underpinnings.
• The philosophical underpinnings of democracy include individual rights.
• Workers installed new underpinnings to stabilize the old structure.
• The scientific underpinnings of the theory have been questioned.