Definition of libration
: an oscillation in the apparent aspect of a secondary body (as a planet or a satellite) as seen from the primary object around which it revolves
Origin of libration
Latin libration-, libratio, from librare to balance, from libra scales
First Known Use: 1667
Learn More about libration
Britannica.com: Encyclopedia article about "libration"
Seen and Heard
What made you want to look up libration? Please tell us where you read or heard it (including the quote, if possible).