What does bisector mean?
A bisector is something that cuts a whole into two exactly equal parts — most commonly a line, ray, or plane in geometry. In school mathematics, the term usually refers to an angle bisector, which splits an angle into two angles of equal measure, or to a perpendicular bisector, which crosses a line segment at its midpoint at a right angle. Both are foundational objects: angle bisectors are central to constructions with compass and straightedge, while perpendicular bisectors underpin ideas such as circumcircles and points equidistant from two locations. Beyond elementary geometry, the word extends naturally to higher dimensions, where a bisector plane may divide a solid or a set of points symmetrically. Though technical in flavour, "bisector" is unambiguous and widely taught, making it a reliable piece of mathematical vocabulary for students and general readers alike.
nounA line, ray, or plane that divides something — typically an angle or a line segment — into two equal parts.
- A line, ray, or plane that divides an angle or line segment into two equal parts (geometry).
- By extension, any line or plane dividing a shape or space into two congruent halves.
"The perpendicular bisector of the segment passes through its midpoint at a right angle."
"To construct an equilateral triangle, first draw the angle bisector of one of its sixty-degree angles."
"The plane bisector split the crystal cleanly into two mirror-image halves."
Regular plural formed by adding -s.
"The three angle bisectors of any triangle meet at a single point called the incenter."
Every angle has exactly one internal bisector — the invisible line Euclid proved you can draw with nothing but a compass and straightedge.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of bisector
"Bisector" derives from Latin "bi-" ("two") plus "secare" ("to cut"), via the Late Latin verb form underlying English "bisect," which entered English around the seventeenth century. The agent-noun suffix "-or" marks the thing that performs the cutting. The root "secare" also gives English words such as "dissect," "intersect," and "section," all sharing the idea of cutting.
Related word forms
How bisector is actually used
"Bisector" is a technical term used almost exclusively in mathematics, especially geometry; it is neutral in register and appears mainly in textbooks, exams, and academic writing. The most frequent collocations are "angle bisector" and "perpendicular bisector." In everyday conversation the verb "bisect" is far more common than the noun.
Easily confused with bisector
"Bisect" is the verb meaning to divide into two equal parts, while "bisector" is the noun naming the thing that does the dividing.