Equilibrium \E`qui*lib"ri*um\, n.; pl. E. Equilibriums, L. Equilibria. [L. aequilibrium, fr. aequilibris in equilibrium, level; aequus equal + libra balance. See Equal, and Librate.]

1. Equality of weight or force; an equipoise or a state of rest produced by the mutual counteraction of two or more forces.

2. A level position; a just poise or balance in respect to an object, so that it remains firm; equipoise; as, to preserve the equilibrium of the body.

Health consists in the equilibrium between those two powers. --Arbuthnot.

3. A balancing of the mind between motives or reasons, with consequent indecision and doubt.

Equilibrium valve (Steam Engine), a balanced valve. See under Valve.

Source: Webster's Revised Unabridged Dictionary (1913)