The tendency to stay as it is under disturbance. Stability is not stillness; it is returning after being pushed.
Latin stabilitas (firmness, steadfastness), from stabilis (able to stand), from stare (to stand); the word for standing firm always meant returning to a stand, not never being moved.
The tendency to return to a held shape after being disturbed, not the absence of disturbance. What is stable has already been pushed and has already come back.