1. (

• stamina ,
• staying_power ,
• toughness ,

) enduring strength and energy ;

2. (

• huskiness ,
• ruggedness ,
• toughness

) the property of being big and strong ;

3. (

• temper ,
• toughness ,

) the elasticity and hardness of a metal object; its ability to absorb considerable energy before cracking ;

4. (

• formidability ,
• toughness ,

) impressive difficulty ;