OXFORD DICTIONARY
perpendicular, adj. & n.
--adj.
1 a at right angles to the plane of the horizon. b (usu. foll. by to) Geom. at right angles (to a given line, plane, or surface).
2 upright, vertical.
3 (of a slope etc.) very steep.
4 (Perpendicular) Archit. of the third stage of English Gothic (15th-16th c.) with vertical tracery in large windows.
5 joc. in a standing position.
--n.
1 a perpendicular line.
2 a plumb-rule or a similar instrument.
3 (prec. by the) a perpendicular line or direction (is out of the perpendicular).
perpendicularity n. perpendicularly adv.
ME f. L perpendicularis f. perpendiculum plumb-line f. PER- + pendere hang
THESAURUS
perpendicular
air line, axis, azimuth circle, beeline, chord, diagonal, diameter, direct line, directrix, edge, erect, great-circle course, normal, orthodiagonal, orthogonal, orthometric, plumb, plunging, precipitous, radius, radius vector, rectangular, right angle, right line, right-angle, right-angled, right-angular, secant, segment, sheer, shortcut, side, stand-up, steep, straight, straight course, straight line, straight stretch, straight-up, straight-up-and-down, straightaway, streamline, tangent, transversal, up-and-down, upright, vector, vertical, vertical circle
ROGET THESAURUS
perpendicular
Verticality
N
verticality, erectness, perpendicularity, right angle, normal, azimuth circle, wall, precipice, cliff, elevation, erection, square, plumb line, plummet, vertical, upright, erect,
perpendicular, plumb, normal, straight, bolt, upright, rampant, standing up, rectangular, orthogonal, vertically, up, on end, up on end, right on end, a plomb, endwise, one one's legs, at right angles.
Perpendicularity
N
perpendicularity, orthogonality, verticality, orthogonal,
perpendicular, rectangular, uncorrelated.