Lewis & Short

aequĭlībrĭum, ii, n. [aequilibris],

  1. I. a level or horizontal position, equilibrium: quaedam ligna ad medium submersa ad aequilibrium aquae, Sen. Q. N. 3, 25; so Col. Arb. 5, 2.
  2. II. Trop., a perfect equality: rumpendi pariter membri, Gell. 20, 1.