Stability was a condition of balance or equilibrium.

In 2096, Australia was one of the most stable nations on Earth. (PROSE: The Indestructible Man)

The Third Doctor helped Lord Roche move the planet Caresh into a closer, more stable orbit around Ember. (PROSE: The Suns of Caresh)

After the Empress collided with the Hecate, the Continuous Event Transmuter became unstable. This allowed Stott and the Mandrels stored in the Eden sample in the CET to escape. (TV: Nightmare of Eden)

An anti-matter-powered spaceship could only be stable if the ship itself were molecularly stable — otherwise, it would explode. (TV: Earthshock)

Rho mesons were a subatomic particle that was the unstable factor in pin galaxies. (TV: The Two Doctors)

Amaranths contained an emergency function to transport its user to a more stable part of space. (PROSE: Christmas on a Rational Planet)

The Daleks wanted to destroy Daleks in all other parallel universes. They used Crivello's Cauldron to create a stable time rift to access those other universes. (COMIC: Fire and Brimstone)

The Krikoosh had the ability to pass through solid matter by making molecules unstable. (COMIC: Extermination of the Daleks)

The Flesh was unstable, allowing some gangers to extend their limbs, their jaw and their neck or in one case, physically mutate their body into a monstrous form. (TV: The Almost People)

An expedition was sent to the Earth's Moon in 2049 to determine why it had become unstable. (TV: Kill the Moon)

In an alternate universe, Low Town was a Gallifreyan shanty town that grew up around the columns that kept the Capitol dome stable. (PROSE: The Infinity Doctors)