| Perpendicular 1. (a.) Exactly upright or vertical; at right angles to the horizon or another object; extending in a right line from any point toward the center of the earth. 2. (a.) At right angles to a given line or surface; as, the line ad is perpendicular to the line bc. 3. (n.) A line at right angles to the plane of the horizon; a vertical line or direction. 4. (n.) A line or plane falling at right angles on another line or surface, or making equal angles with it on each side. Thesaurus Entries 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 |