planityrare—1.|ˈplænɪtɪ| [f. plane a. + -ity. (Cf. L. plānitās plainness, a doubtful reading in Tacitus.)] The quality of being plane. 1882Proctor Fam.Sci.Stud. 21 The straightness of lines, the planity of surfaces and other like geometrical conceptions.