libration

plural librations

1. countableuncountableThe act of librating.
2. countableuncountableastronomyThe apparent wobble or variation in the visible side of the Moon that permanently faces the Earth, allowing observers on Earth to see, over a period of time, slightly more than half of the lunar surface.
3. broadlycountableuncountableA similar rotational or orbital characteristic of some other celestial body.
4. countableuncountabledynamicsThe oscillation of an angle about a stable equilibrium point.
5. countableuncountablechemistryA vibrational degree of freedom whereby a group of atoms partly rotates back and forth, similar to the Moon's motion.
6. countablefigurativelyuncountableA wavering between two opposing thoughts or choices.

   We may not quarrel with attempts to picture the libration of emotion which sways Clytaemestra as she veers from love for her husband to the desire to take vengeance upon him[…]

   1924, Herbert Weir Smyth, “VI. Orestea. I: Agamemnon”, in Aeschylean Tragedy, page 175