early 15c., from Latin explanare "to explain, make clear, make plain" (see explanation). Originally explane, spelling altered by influence of plain. Also see plane, v.2. In 17c., occasionally used more literally, of the unfolding of material things: Evelyn has buds that "explain into leaves" ["Sylva, or, A discourse of forest-trees, and the propagation of timber in His Majesties dominions," 1664]. Related: Explained; explaining; explains. To explain (something) away is from 1709.