equilibrium

What it means

1. The condition of a system in which competing influences are balanced, resulting in no net change.

   To Hydroſtaticks belong whatever relates to the Gravities and Equilibria of Liquors; with the Art of weighing Bodies in Water, in order to eſtimate the ſpecifick Gravities.

   1733, Philip Miller, “HYDROSTATICKS”, in The Gardeners Dictionary: […], 2nd edition, volume I, London: […] C[harles] Rivington, […], →OCLC, column 1

   1 more example

   1999, The Matrix, Agent Smith speech Every mammal on this planet instinctively develops a natural equilibrium with the surrounding environment but you humans do not. You move to an area and you multiply and multiply until every natural resource is consumed and the only way you can survive is to spread to another area. There is another organism on this planet that follows the same pattern. Do you know what it is? A virus.

   Synonyms: balance, stability · Antonyms: disequilibrium, imbalance, instability

2. Mental balance.

   Tiffany Pollard: What just happened?! Eric Andre: That coffee mug is broken. Tiffany Pollard: I can't take this. This is gonna mess up my equilibrium.

   2020, The Eric Andre Show, season 5, episode 6

   Synonyms: sanity · Antonyms: insanity, instability, madness

3. chemistryThe state of a reaction in which the rates of the forward and reverse reactions are the same.

In a sentence

To Hydroſtaticks belong whatever relates to the Gravities and Equilibria of Liquors; with the Art of weighing Bodies in Water, in order to eſtimate the ſpecifick Gravities.

1733, Philip Miller, “HYDROSTATICKS”, in The Gardeners Dictionary: […], 2nd edition, volume I, London: […] C[harles] Rivington, […], →OCLC, column 1

Where it comes from

1. Latinaequilībrium
2. Englishequilibrium

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