equilibrium

Pronunciation

• UK: /ɛkwɪˈlɪbɹɪəm/, /iːkwɪˈlɪbɹɪəm/^[1]

Etymology

It is borrowed from Latin aequilībrium (“an even balance; a horizontal position”),^{[2][3][4][5][6]} from aequilībris (“level, evenly balanced”),^[3][7] formed from aequus (“equal”) and lībra (“a balance, pair of scales, plummet”),^[3][4][2][8] itself of uncertain origin.^[4] The first part, aequus, is also the source of equal.^[3]

Earliest recorded meaning

A well-balanced state of mind or feeling, poise: 1608, in a sermon by Bishop J. King at St Mary's, Oxford.^[2][6][9] Etymonline dates the word to about 1600 in this sense.^[3]

Semantic evolution

The physical sense, the balance between opposing forces acting on a body, is recorded from 1660, in Boyle's New Experiments Physico-mechanicall.^[2] By 1677 it was applied more widely to a balance between powers of any kind, and by 1685 to the suspense or indecision that equally strong motives produce.^[2][6] Johnson (1755) defined it as "equipoise; equality of weight" and, secondly, as equality of evidence or motives.^[10] The Latin phrase in aequilibrio, in equilibrium, was used in English from 1650, usually spelled in equilibrio.^[2][10] In economics, from 1871 in Jevons, it is a state in which supply and demand are matched and prices are stable.^[2][6] The chemical sense, a reversible reaction in which the two directions go on at equal rates, is listed by the modern dictionaries.^[11][7][12]

Timeline

• 1608 – a well-balanced state of mind.^[2][7]
• 1650 – the Latin phrase in equilibrio.^[2]
• 1660 – a balance between opposing physical forces, in Boyle.^[2]
• 1677 – a balance between powers of any kind.^[2]
• 1685 – indecision produced by equally strong influences.^[2]
• 1871 – in economics, supply and demand in balance, in Jevons.^[2]

Meanings

Noun

1. A state of balance in which opposing forces or influences cancel each other out, so that nothing changes: The two populations reached an equilibrium.^[11][12][7]
2. In physics, the state of a body at rest or in uniform motion, with no resulting force acting on it.^[11][12][7]
3. In chemistry, the state of a reversible reaction in which the forward and reverse reactions go on at the same rate.^[11][12][7]
4. Mental or emotional balance; composure or poise: She lost her equilibrium for a moment.^[11][12][6]
5. In economics, a state in which supply and demand are matched and prices are stable.^[6][2]

Word family

• nonequilibrium
• disequilibrium
• equilibrist
• equilibrium constant
• equilibrium price
• punctuated equilibrium

Related words

• equilibrate
• equivalence
• equal
• Libra
• equi-

References

1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f g h i j k l m n Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ a b c d e Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
4. ^ a b c Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
5. ^ The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt
6. ^ a b c d e f Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
7. ^ a b c d e f Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
8. ^ Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
9. ^ Stevenson, Angus, ed. (2010), Oxford Dictionary of English, 3rd ed., Oxford: Oxford University Press
10. ^ a b Johnson, Samuel (1755), A Dictionary of the English Language, London; 4th ed. 1773; Johnson's Dictionary Online, ed. Beth Rapp Young et al.
11. ^ a b c d e The American Heritage Dictionary of the English Language (1992), 3rd ed., Boston: Houghton Mifflin
12. ^ a b c d e Collins English Dictionary (2023), Glasgow: HarperCollins