un·sta·ble 
(ŭn-stābəl)
(ŭn-stābəl)adj. un·sta·bler, un·sta·blest
1.
a. Tending strongly to change: unstable weather.
b. Not constant; fluctuating: unstable vital signs.
2.
a. Wavering or fickle: At first, he was unstable in his decisions.
b. Showing or marked by erratic or volatile emotions or behavior.
3. Not firmly placed; unsteady: an unstable ladder.
4. Chemistry
a. Decomposing readily.
b. Highly or violently reactive.
5. Physics
a. Decaying with relatively short lifetime. Used of subatomic particles.
b. Radioactive.
un·stable·ness n.
un·stably adv.