toughness

(mechanics) A property of a material capable of absorbing energy by plastic deformation; intermediate between softness and brittleness.

noun

1. The fact or condition of being rigorous and unsparing: austerity, hardness, harshness, rigidity, rigor, rigorousness, severity, sternness, strictness, stringency. See easy/hard.
2. Unwavering firmness of character, action, or will: decidedness, decision, decisiveness, determination, firmness, purpose, purposefulness, resoluteness, resolution, resolve, will, willpower. See certain/uncertain, strong/weak.

For a material, its ability to absorb energy.

The noun has 4 meanings:

Meaning #1: enduring strength and energy
  Synonyms: stamina, staying power

Meaning #2: the property of being big and strong
  Synonyms: huskiness, ruggedness

Meaning #3: the elasticity and hardness of a metal object; its ability to absorb considerable energy before cracking
  Synonym: temper

Meaning #4: impressive difficulty
  Synonym: formidability