unstable
adj.adj. likely to change, fall, or fail suddenly. You use this to describe things that are not steady or safe, like a shaky chair or a person's changing mood.
adj. prone to change, failure, or collapse; lacking stability. In scientific contexts, it describes substances or systems that undergo spontaneous change or decay.
The old wooden ladder feels very unstable.
The country's economy remained unstable for years following the sudden collapse of its largest bank.
Chemical compounds that are highly unstable must be stored at extremely low temperatures to prevent them from reacting or decomposing unexpectedly.
From Middle English unstable; equivalent to un- (not) + stable.
From un- (reversive prefix) + stable.
Often used to describe physical structures, emotional states, or volatile chemical substances.