- Not stable, by either of its definitions. Unstable equilibrium arises when there are multiple equilibria, as in the case of inelastic offer curves that intersect three times instead of once. The middle equilibrium is unstable.
- Not tending to remain in a given position, state, setting, mode, or the like. For instance, unstable oscillation.
- Not tending to return to a former or desired position, state, setting, mode, or the like, after a displacement or other change occurs. For example, a speaker with improper damping.
- Not tending to maintain a given value, quantity, intensity, characteristic, or the like.
- Tending to easily respond to a change, action, stimulus, or variation.
- A chemical substance which easily forms part of a chemical reaction.
- A particle or isotope which exhibits radioactive decay.
- adjective referring to something which may change easily