Lewis & Short

lībrātĭo, ōnis, f. [libro].

  1. I. A making level, levelling: fortasse qui Archimedis libros legit, dicet non posse fieri veram ex aqua librationem, Vitr. 8, 6, 3.
  2. II. A horizontal position, level: circa terrae librationem, Vitr. 6, 1, 5.
  3. III. A hurling off, hurling, slinging, Diom. p. 473 P.