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unstable

Etymology and origin of the English word unstable

History Permalink
Confidence
Established
Formation
Derivation
First attested
c. 1200
Ultimate origins
English (un-)Old French (estable)
Etymology tree
inherited borrowed derived
English stable
English unstable

Pronunciation

  • IPA: /ʌnˈsteɪ.bəl/[1]

Etymology

It is from English un- + stable.[2][3] A similar formation is Middle High German unstabel.[2]

Earliest recorded meaning

Apt to move, not staying steadily in place: about 1200 in Etymonline, before 1225 in the OED.[2][4]

Semantic evolution

Fickle, vacillating or changeable is from the late 13th century (about 1290),[2][4] liable to fall from about 1300,[2] and structurally insecure by the late 14th century.[2] Not fixed in condition, exposed to chance, is from about 1340.[4] Technical senses follow: unstable equilibrium in mechanics (1839), unstable compounds in chemistry (1849) and in physics (1904).[4] An Old English word for the idea was feallendlic.[2]

Timeline

  • c. 1200 – apt to move.[2]
  • c. 1290 – fickle.[4]
  • c. 1300 – liable to fall.[2]
  • 1849 – unstable compounds.[4]

Modern meaning

Adjective

  1. Likely to change or fail; not stable or firm.
  2. Not firmly fixed; likely to fall or give way.
  3. Of a person, given to unpredictable changes of mood or behaviour.
  4. (chemistry, physics) Readily decomposing or decaying, as a radioactive substance.

Word family

  • unstableness
  • unstably

References

  1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
  2. ^ a b c d e f g h i Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
  3. ^ Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
  4. ^ a b c d e f Simpson, J. A.; Weiner, E. S. C., eds. (1989), The Oxford English Dictionary, 2nd ed., Oxford: Clarendon Press
Cite this entry

“Unstable.” Etymologically, 17 Oct. 2026, etymologically.com/en/unstable. Accessed 17 Oct. 2026.

Last edited on . ·