unstable

adj

1. Not stable.

   “unstable foundation”

   “The structure is too unstable to stand safely.”

   “The hillside at this point is composed of shaly rock overlaid with a peaty loam which carries a growth of heather, and its unstable condition has resulted in two landslides in the course of the railway's history.”

2. 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.”

3. Fluctuating; not constant.

   “politically unstable”

   “The political situation remains unstable.”

4. (figuratively)Fickle.
5. (figuratively)Unpredictable.

   “All of the characters in Rocko's Modern Life are anthropomorphic animals of varying species, the vast majority of whom are mentally unstable. Murray said that he matched personalities of his characters to the various animals in the series to form a social caricature.”

6. Readily decomposable.

   “chemically unstable”

7. Radioactive, especially with a short half-life.

verb

1. (transitive)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.”