perpendicular

American Heritage® Dictionary of the English Language, Fourth Edition

1. adj. Mathematics Intersecting at or forming right angles.
2. adj. Being at right angles to the horizontal; vertical. See Synonyms at vertical.
3. adj. Of or relating to a style of English Gothic architecture of the 14th and 15th centuries, characterized by emphasis of the vertical element.
4. adv. In a perpendicular position.
5. n. Mathematics A line or plane perpendicular to a given line or plane.
6. n. A perpendicular position.
7. n. A device, such as a plumb line, used in marking the vertical from a given point.
8. n. A vertical or nearly vertical line or plane.

Century Dictionary and Cyclopedia

1. Perfectly vertical; at right angles with the plane of the horizon; passing (if extended through the center of the earth; coinciding with the direction of gravity.
2. In geometry, meeting a given line or surface (to which it is said to be perpendicular) at right angles. A straight line is said to be perpendicular to a curve or surface when it cuts the curve or surface in a point where another straight line to which it is perpendicular is tangent to the curve or surface. In this case the perpendicular is usually called a normal to the curve or surface.
3. In zoology, forming a right angle with the longitudinal or latitudinal axis of the body: as, a perpendicular head; epimeron perpendicular, etc.
4. n. A line at right angles to the plane of the horizon; a line that coincides in direction with a radius of the earth or with the direction of gravity.
5. n. 2. In geometry, a line that meets another line or a place at right angles, or makes equal angles with it on every side. Thus, if the straight line AB, falling on the straight line CD, makes the angles ABC, ABD equal to one another, AB is called a perpendicular to CD, and CD is a perpendicular to AB. A line is a perpendicular to a plane when it is perpendicular to all lines drawn through its foot in that plane.
6. n. In gunnery, a small instrument for finding the center-line of a piece of ordnance, in the operation of pointing it at an object; a gunner's level.
7. n. In ship-building, one of the three conventional lines perpendicular to the line of the keel, used as reference lines from which measurements in the fore-and-aft direction are taken. The conventional points through which these perpendiculars are passed vary. The forward perpendicular in old wooden vessels was at the intersection of the bottom line of the rabbet of the stem with the line of the lower deck. In modern practice in iron vessels it is usually at the intersection of the forward side of the stem with the normal load water-line, and this is its prescribed position in the United States navy. The after perpendicular, in wooden vessels, was at the intersection of the bottom line of the rabbet of the sternpost with the line of the lower deck. In modern vessels it is usually taken at the intersection of the after side of the rudder-post with the normal load-line, though it is sometimes taken through the axis of the rudder-stock. In the United States navy, however, it is taken at the intersection of the normal load water-line with the contour of the stern. The middle perpendicular, much less used than the other two, is midway of the length between the forward and after perpendiculars. The length between perpendiculars is the length of the vessel measured parallel to the keel between the forward and the after perpendiculars.

Wiktionary

1. adj. geometry At or forming a right angle (to).
2. n. geometry A line or plane that is perpendicular to another.
3. n. A device such as a plumb line that is used in making or marking a perpendicular line.

GNU Webster's 1913

1. adj. 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.
2. adj. (Geom.) At right angles to a given line or surface.
3. n. A line at right angles to the plane of the horizon; a vertical line or direction.
4. n. (Geom.) A line or plane falling at right angles on another line or surface, or making equal angles with it on each side.

WordNet 3.0

1. n. a straight line at right angles to another line
2. n. a cord from which a metal weight is suspended pointing directly to the earth's center of gravity; used to determine the vertical from a given point
3. adj. at right angles to the plane of the horizon or a base line
4. adj. intersecting at or forming right angles
5. n. a Gothic style in 14th and 15th century England; characterized by vertical lines and a four-centered (Tudor) arch and fan vaulting
6. n. an extremely steep face
7. adj. extremely steep