unstable

Not stable.

unstable foundation

The structure is too unstable to stand safely.

Having a strong tendency to change.

The dawn of the oil age was fairly recent. Although the stuff was used to waterproof boats in the Middle East 6,000 years ago, extracting it in earnest began only in 1859 after an oil strike in Pennsylvania.[…]It was used to make kerosene, the main fuel for artificial lighting after overfishing led to a shortage of whale blubber. Other liquids produced in the refining process, too unstable or smoky for lamplight, were burned or dumped.

Fluctuating; not constant.

politically unstable

The political situation remains unstable.

Fickle.

Unpredictable.

To release (an animal) from a stable.

When the last tune of music floated from the fleet, he unstabled his quarter horse and headed for the coastal road leading west and north on his circuit.