稳固 means 'stable, firm, solid' and emphasizes that something is securely established and unlikely to move or collapse. Compared to the more general 稳定 (steady, stable), 稳固 conveys a stronger sense of physical or structural security, often used for foundations, relationships, or a country's economy. The verb sense 'to stabilize' implies making something solidly fixed, distinct from 巩固 (to consolidate) which is an active process of strengthening.