WordWeb Online

1. Enduring strength and energy
   "lacking in toughness";
   - stamina, staying power, stickability [informal]
    
2. The property of being big and strong
   - huskiness, ruggedness
    
3. The elasticity and hardness of a metal object; its ability to absorb considerable energy before cracking
   - temper
    
4. Impressive difficulty
   - formidability

Type of: difficultness, difficulty, elasticity, endurance, fix [informal], hole [informal], jam [informal], kettle of fish [informal], mess [informal], muddle [informal], pickle [informal], snap, strength

Encyclopedia: Toughness