Unstable

Part of speech: adjective

Pronunciation: /ʌnˈsteɪ.bəl/

Definitions

1. Lacking firmness, steadiness, or balance; prone to sudden changes or likely to collapse
2. Not firmly fixed or steady, leading to frequent abrupt changes or potential failure in maintaining equilibrium
3. Not steady or solid, easily moved or likely to fall over ; liable to change quickly without warning in condition or behavior

Etymology: "Unstable" is a plain compound: the negating prefix "un-" attached to "stable," which itself came into Middle English from Anglo-Norman "stable," borrowed from Latin "stabulum," a word for a standing place such as a stall or dwelling. The root idea is standing firm, which is why a stable thing is one that stays put. The prefix "un-" does the work of reversal here, turning "stable" into its opposite. English has long used this device freely, so "unstable" needed no special coinage: once "stable" meant firmly fixed, its negation followed naturally. Its sense of abrupt, unpredictable change grew out of the physical idea of something that will not stay upright or in place. Note that "unstable" sits alongside "instable," a near-twin formed from Latin negation rather than English "un-," and "astable," which shares the same negating logic from Greek. The three words are doublets in the loose sense that they express the same idea through different routes into English.

Synonyms: volatile, precarious, insecure, unsteady

Antonyms: stable, steady, secure