sternness

/ˈstɜːrn.nəs/
noun
  1. The quality of being serious, strict, or severe in manner or appearance.
    • Her sternness softened when she saw the puppy's sad eyes.
    • The teacher's sternness made the students quiet down immediately.
    • The judge's sternness was meant to show that the court would not tolerate dishonesty.