fastness

/ˈfæstnəs/
noun
  1. A secure or fortified place; a stronghold.
    • The castle was a fastness that had never been conquered.
    • The rebels retreated to their mountain fastness.
    • The ancient fastness stood guard over the valley for centuries.
  2. The quality of being fast, quick, or speedy.
    • The fastness of her reflexes saved her from the falling branch.
    • He was amazed by the fastness of the new computer processor.
    • The fastness of the cheetah is legendary.
  3. The quality of being firmly fixed or secure; stability or resistance to change (e.g., colorfastness).
    • The fastness of the glue ensured the shelf stayed attached to the wall.
    • The dye's fastness to sunlight made it ideal for outdoor fabrics.
    • Test the color fastness of the shirt before washing it with whites.
Antonyms
What does "fastness" mean? | whatsthatwordmean | whatsthatwordmean