1. the quality or state of being solid, firm, or stable
2. the quality of being reliable, dependable, or well-founded

Examples

• The solidness of the foundation ensured the building would last for decades.
• She admired the solidness of the oak table her grandfather had built.
• The solidness of his argument convinced even the skeptics.
• The bridge’s solidness was tested during the earthquake.
• His reputation for solidness made him a trusted business partner.
• The solidness of their friendship had endured many challenges.
• The rock’s solidness made it perfect for the sculpture.