1. The quality of being steady or securely and immovably fixed in place
   "The firmness of the foundation ensured the building's stability";
   - steadiness
    
2. The trait of being resolute
   "his firmness carried him through the battle";
   - resoluteness, firmness of purpose, resolve, resolution
    
3. The property of being unyielding to the touch
   "The firmness of the mattress provided excellent back support"
    
4. The muscle tone of healthy tissue
   "his muscular firmness";
   - soundness

Type of: hardness, immovability, immovableness, strength, trait

Antonym: ricketiness