English Reference
noun

equilibrium

n.
US /ˌikwəˈɫɪbɹiəm/ UK /ˌiːkwɪlˈɪbɹiəm/ equi·lib·ri·um UK spelling equilibriums

  1. 01 C1 Advanced Academic Science

    a state where different parts or forces are balanced and stable.

    a condition in which all acting influences are cancelled by others, resulting in a stable, balanced, or unchanging system.

    Simple

    The scales reached equilibrium when the weights on both sides were exactly the same.

    In context

    The ecosystem maintained a delicate equilibrium for centuries until the introduction of invasive species disrupted the local food chain.

    Usage

    Often used with the verbs 'maintain', 'disturb', or 'restore'.

  2. 02 C1 Advanced Technical Science

    the point in a chemical reaction where the forward and backward changes happen at the same speed.

    the state of a reversible chemical reaction in which the rates of the forward and reverse reactions are equal, resulting in no net change in concentrations.

    Simple

    In a closed bottle of soda, the liquid and gas reach equilibrium.

    In context

    The chemist adjusted the temperature to shift the equilibrium of the reaction, thereby increasing the yield of the desired product.

    chemical balance
  3. 03 C2 Proficiency FormalLiterary

    a calm state of mind where you feel balanced and in control.

    a state of emotional or mental balance; composure.

    Simple

    Yoga helps her recover her equilibrium after a stressful day at the office.

    In context

    It took several months of quiet reflection for him to regain his mental equilibrium following the sudden collapse of his business empire.

Usage restore equilibrium

Consider the heat flow, and what happens when the system of sun, blinds and curtain reaches its equilibrium.

The Guardian· 20 Jul 2026

The analysis further argues that comparisons with trophic cascades around the world relied on equilibrium assumptions that do not fit Yellowstone's still recovering, non equilibrium ecosystem.

ScienceDaily· 14 Jun 2026

From Latin aequilībrium, from equal + lībra (“balance”).

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

This entry
Level C1 · Advanced
Frequency Frequent
Updated