1510s, from L. explanare "to make level, smooth out;" also "to explain, make clear" (see explanation
). Originally explane, spelling altered by influence of plain. 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.