坚固 (jiāngù) is an adjective meaning 'solid', 'sturdy', or 'robust' — describing something that is physically strong, well-built, and resistant to damage or wear. The character 坚 (jiān) means 'firm', 'resolute', or 'hard', often implying strength of structure or will; 固 (gù) means 'solid', 'stable', or 'fixed', suggesting firmness in position or composition. Together, they emphasize structural integrity and durability, not just hardness but reliable resistance to pressure, impact, or decay.

This word is commonly used to describe buildings, bridges, tools, furniture, containers, and other man-made objects where safety and longevity matter. It appears frequently in engineering, construction, product descriptions, and everyday evaluations of quality ('This suitcase is very坚固'). While it can occasionally describe abstract concepts like 'a坚固 alliance', such usage is rare and stylistically marked — the primary sense remains physical robustness.