A solid structure refers to a sturdy and robust formation that can withstand external forces and maintain its shape and form over time. Some of the synonyms for a solid structure include sound, durable, secure, steadfast, unyielding, resolute, firm, stable, reliable, and substantial. Each of these words implies the strength and integrity of a well-built structure. A sound structure refers to a solid foundation, while a sturdy structure implies strength and toughness. A secure structure is free from danger and risks, while a steadfast structure suggests resilience and firmness. An unyielding structure can withstand pressure and force, while a resolute structure demonstrates a strong and determined character. Finally, a firm, stable, reliable, and substantial structure all conveys the idea of a solid and sturdy formation that can be trusted and depended upon for its strength and consistency.