noun 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.
noun A similar rotational or orbital characteristic of some other celestial body.
noun The oscillation of an angle about a stable equilibrium point.
noun A vibrational degree of freedom whereby a group of atoms partly rotates back and forth, similar to the Moon's motion.
noun A wavering between two opposing thoughts or choices.