WordWeb Online

1. The muscle tone of healthy tissue
   "his muscular firmness";
   - soundness
    
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
    
4. The quality of being steady or securely and immovably fixed in place
   - steadiness

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

Antonym: unsteadiness