The Collaborative International Dictionary of English v.0.48:

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.
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   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.
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            Health consists in the equilibrium between those two
            powers.                               --Arbuthnot.
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   3. A balancing of the mind between motives or reasons, with
      consequent indecision and doubt.
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   Equilibrium valve (Steam Engine), a balanced valve. See
      under Valve.
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