Plane1  —n. 1 flat surface such that a straight line joining any two points on it lies wholly in it. 2 level surface. 3 colloq. = *aeroplane. 4 flat surface producing lift by the action of air or water over and under it (usu. In comb.: hydroplane). 5 (often foll. By of) level of attainment, knowledge, etc. —adj. 1 (of a surface etc.) Perfectly level. 2 (of an angle, figure, etc.) Lying in a plane. —v. (-ning) glide. [latin planus *plain]