noun
- a secure or fortified place; stronghold: a mountain fastness.
- the state of being fixed or firm: the fastness of democratic institutions.
- the state of being rapid.
noun
- a stronghold; fortress
- the state or quality of being firm or secure
- the ability of a dye to remain permanent and not run or fade
- archaic swiftness
“a place not easily forced, a stronghold,” late Old English fæstnes, from fast (adj.) in its older sense of “firm, fixed in place” + -ness.