Definitions
1.nounThe act of librating.
2.nounThe 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.noun(by extension) A similar rotational or orbital characteristic of some other celestial body.
4.nounA vibrational degree of freedom whereby a group of atoms partly rotates back and forth, similar to the Moon's motion.