Definition
Equilibrium is balance with effort hidden inside it. From the Latin aequus (equal) and libra (scales), it names the state in which opposing forces cancel so exactly that nothing moves: supply meets demand, predator balances prey, the diver's body steadies between buoyancy and weight. Equilibrium is not the absence of forces but their perfect answer to each other — which is why disturbing one side sets the whole system searching for balance again.
Examples
- Prices stabilize when supply and demand reach equilibrium.
- The ecosystem maintained a delicate equilibrium between predators and prey.
- After weeks of upheaval, the team finally recovered its equilibrium.
Synonyms
balance · stability · steadiness · symmetry · poise
In TOEFL & IELTS
Indispensable for TOEFL science passages — chemical equilibrium, ecological equilibrium, market equilibrium all recur. The phrase 'punctuated equilibrium' appears in evolution texts. For IELTS essays, 'strike/maintain a balance' is the everyday register and 'reach an equilibrium' the formal one. Plural, rarely needed: equilibria.