unstable
UK: ʌnˈsteɪbəl | US: ʌnˈsteɪbəl
adj. not firm or fixed; likely to change or fail
adj. prone to emotional or mental unpredictability
adj. (chemistry/physics) readily decomposing or reacting
The word "unstable" combines the Old English prefix "un-" (meaning "not") with "stable," derived from Latin "stabilis" (firm, steadfast). "Stabilis" itself comes from "stare" (to stand). The fusion reflects a logical negation: "not standing firm." Over time, its meaning expanded from physical instability (e.g., wobbly structures) to abstract contexts like emotions or chemical reactions.
The old chair was unstable and collapsed under his weight.
Her mood became unstable after the stressful news.
This chemical compound is highly unstable at room temperature.
The political situation in the region remains unstable.
Avoid walking on unstable ground during the hike.