You searched for: “libration”
libration (s) (noun), librations (pl)
A real or apparent oscillation in the orbit of one celestial body as seen from the one around which it orbits; especially, as seen in the Moon from the Earth.
This entry is located in the following units: -ation, -ization (-iz[e] + -ation); -isation (British spelling variation) (page 59) libra-, liber-, libri- (page 2)