equilibrium (English)

Where does "equilibrium" come from?

The English word 'equilibrium' comes from the Latin noun 'aequilībrium'[1][2]. This Latin term is formed from 'aequus', meaning level or even, combined with 'lībra', meaning a level or balance, along with the suffix '-ium'[2]. The component 'aequus' shares a root with the Middle English word 'equal', which stems from Latin 'aequālis'[3]. Meanwhile, the origin of the Latin word 'lībra' is uncertain[4].

Open questions

• The ultimate origin of the Latin word libra is uncertain, with proposed reconstructions suggesting an earlier Proto-Italic form and a derivation from Proto-Indo-European related to pouring metal. [4]

Full etymology tree

• equilibrium (English), 'The condition of a system in which competing influences are balanced, resulting in no net change.'
  • borrowed aequilibrium (Latin), 'A level or horizontal position, equilibrium.'
    • compound aequus (Latin), 'equal'
    • compound libra (Latin), 'libra, Roman pound, a Roman unit of mass, equivalent to about 327 g'
      • inherited *līðrā (Proto-Italic), 'ingot'
        • derived *leyH- (Proto-Indo-European)
        • suffix *-dʰrom (Proto-Indo-European), 'alternative form of *-trom'
    • suffix -ium (Latin), 'Suffix used to form abstract nouns, sometimes denoting offices and groups. May no longer be productive.'

Descendants and derived words

• acid-base equilibrium (English)
• chemical equilibrium (English)
• disequilibrium (English)
• dynamic equilibrium (English)
• dynamic stochastic general equilibrium (English)
• dysequilibrium (English)
• economic equilibrium (English)
• equilibrist (English)
• equilibrium constant (English)
• equilibrium price (English)
• equilibrium time (English)
• equilibrium vapor pressure (English)

Sources

1. equilibrium (English) - Wiktionary
2. aequilibrium (Latin) - Wiktionary
3. equal (English) - Wiktionary
4. libra (Latin) - Wiktionary

Updated August 2026

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Etymology data from Wiktionary, CC BY-SA 4.0 · About Miraris