libration

noun6

1. •
   The act of librating.
2. •
   The 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. •
   A similar rotational or orbital characteristic of some other celestial body.
4. •
   The oscillation of an angle about a stable equilibrium point.
5. •
   A vibrational degree of freedom whereby a group of atoms partly rotates back and forth, similar to the Moon's motion.
6. •
   (figurative) A 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