- (n.) A line at right angles to the plane of the horizon; a vertical line or direction.
- (a.) At right angles to a given line or surface; as, the line ad is perpendicular to the line bc.
- (a.) Exactly upright or vertical; pointing to the zenith; at right angles to the plane of the horizon; extending in a right line from any point toward the center of the earth.
- (n.) A line or plane falling at right angles on another line or surface or making equal angles with it on each side.
Webster's Revised Unabridged Dictionary
| APA | Webster's. (2011). perpendicular. Retrieved September 20, 2026, from http://smartdefine.org/perpendicular/definitions/2044067 |
| Chicago | Webster's. 2011. "perpendicular" http://smartdefine.org/perpendicular/definitions/2044067 (accessed September 20, 2026). |
| Harvard | Webster's 2011, perpendicular, Smart Define, viewed 20 September, 2026, <http://smartdefine.org/perpendicular/definitions/2044067>. |
| MLA | Webster's. "perpendicular" 27 May 2011. Web. 20 September 2026. <http://smartdefine.org/perpendicular/definitions/2044067> |