Solidnesses refer to the qualities of firmness and stability. There are numerous synonyms for this word, including steadfastness, durability, permanence, and immovability. These terms describe the ability of something to remain strong and reliable over time. Other synonyms for solidnesses include strength, consistency, resilience, and robustness, which describe different aspects of stability. Solidnesses can also refer to the physical state of being solid, in which case the synonyms include density, compactness, and hardness. Regardless of the context, using synonyms for solidnesses is an effective way to add variety to your writing and convey a stronger sense of stability and strength.