What does collinear mean?
Collinear is an adjective describing points, objects, or vectors that lie along one and the same straight line. In geometry, three or more points are said to be collinear if a single straight line can be drawn through all of them — a condition easily tested by checking whether the triangle they would form has zero area. The term also appears in physics and computer graphics, where light rays, forces, or data points may be described as collinear when they share a common line of action or alignment. Its counterpart, noncollinear, signals the absence of such alignment. Derived from Latin roots meaning 'together' and 'line', the word carries a precise, technical register: it is at home in textbooks, proofs, and scientific papers rather than casual conversation. Because any two points are trivially collinear, the term becomes meaningful only when applied to three or more items, making it a compact way to express a strong geometric constraint.
adjectiveLying in or passing through the same straight line; (of points) situated on a single line.
- (of points or objects) Lying on the same straight line.
- (mathematics, of vectors) Parallel to a common line, i.e. scalar multiples of one another.
"The three towns are collinear, so a single highway can connect them all."
"If three points are collinear, the area of the triangle they form is zero."
"In perspective drawing, the vanishing point lies collinear with parallel edges receding into the distance."
Any two points are automatically collinear — it takes a third point to make the property interesting.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of collinear
Collinear derives from the Latin prefix com- ('together, with') combined with linearis, from linea ('line'), itself from linum ('flax, thread'). It entered English as a technical term in mathematics, likely in the 19th century alongside related terms such as linear and lineal, which share the same Latin root. Its cognates include align, lineage, and linear, all tracing back to the idea of a thread or line.
Related word forms
How collinear is actually used
A technical term used chiefly in geometry, physics, and computer graphics; rare in everyday speech. Often appears with the negative form 'noncollinear' when points deliberately do not share a line.
Easily confused with collinear
Coplanar means lying in the same plane, whereas collinear means lying on the same line — collinear points are always coplanar, but coplanar points need not be collinear.