What does perpendicular mean?
Perpendicular describes a line, plane, surface, or direction that meets another at a right angle, or 90 degrees. The most common use is mathematical: a perpendicular line intersects another line at a right angle, and a perpendicular plane meets a plane or line in the corresponding way. In general descriptions, “perpendicular to the ground” means upright, while “perpendicular to the wall” means extending out from it at a right angle. The word can also function as a noun, referring to a perpendicular line or direction, and as an adverb in phrases such as “cut perpendicular to the surface.” Its strength comes from precision: unlike the broader “vertical,” perpendicular always implies a right-angle relationship. It is especially useful in geometry, architecture, construction, design, navigation, and technical drawing, where an exact orientation matters.
At right angles to a line, plane, or surface; upright or directly across in a general context.
"The ship was heading perpendicular to the shoreline."
The mathematical sense is precise; the general sense can imply upright or vertical.
A line or plane that intersects another line or plane at a right angle.
"Draw a perpendicular from the point to the base of the triangle."
Common in geometry and technical description.
At right angles; directly across or squarely.
"The blade must be held perpendicular to the cutting surface."
Usually used in technical or precise contexts, especially with terms such as “cut” or “held.”
The plural is used when referring to multiple perpendicular lines, directions, or other geometric elements.
"The diagram shows three perpendiculars to the horizontal axis."
A perpendicular is defined by a perfect 90-degree angle, making it the geometric ideal of a true right angle.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does perpendicular come from?
The word comes through Old French from the Latin adjective perpendicularis, meaning “at right angles” or “coming down straight.” Its roots are per- “across or through” and pendere “to hang,” reflecting the idea of a line hanging or extending straight across another. The related English noun perpendicularity was also borrowed from Latin, while perpendicularly developed as an adverb in English.
Related word forms
How perpendicular is actually used
In technical and everyday use, perpendicular generally means exactly at a right angle. When no reference line or surface is specified, it can mean upright or vertical, especially in British usage. The noun is common in geometry and in the phrase 'the perpendicular.'
Easily confused with perpendicular
Perpendicular describes lines or planes meeting at a right angle, while parallel describes lines or planes that never meet because they remain the same distance apart.
Vertical means upright in relation to gravity, whereas perpendicular means at right angles to a specified line, plane, or surface.