1. The act of balancing or state of being balanced; a state of equipoise, with equal weights on both sides of a center.
2. In astronomy, an apparent irregularity of the moon's motions, by which it seems to librate about its axis.
Libration is the balancing motion or trepidation in the firmament, whereby the declination of the sun and the latitude of the stars change from time to time.
3. A balancing or equipoise between extremes.