Main Entry: li·bra·tion

Pronunciation: \lī-ˈbrā-shən\

Function: noun

Etymology: Latin libration-, libratio, from librare to balance, from libra scales

Date: 1667

: 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

— li·bra·tion·al \-shnəl, -shə-n^əl\ adjective

— li·bra·to·ry \ˈlī-brə-ˌtȯr-ē\ adjective