Source : Webster's Revised Unabridged Dictionary (1913)

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 : WordNet®

equilibrium
     n 1: a chemical reaction and its reverse proceed at equal rates
          [syn: {chemical equilibrium}]
     2: a stable situation in which forces cancel one another [ant:
        {disequilibrium}]
     3: equality of distribution [syn: {balance}, {equipoise}, {counterbalance}]
     4: a sensory system located in structures of the inner ear that
        registers the orientation of the head [syn: {labyrinthine
        sense}, {vestibular sense}, {sense of balance}, {sense of
        equilibrium}]
     [also: {equilibria} (pl)]