Plural of “vertex”
The plural of vertex is vertices (some dictionaries also accept vertexes).
Why
"Vertex" is Latin for "the highest point" or "whirl" (from "vertere," to turn), and it follows the same Latin -ex/-ices pattern behind "index/indices" and "apex/apices," giving "vertices" as the classical plural — near-universal in geometry, where it describes the point where two or more edges of a shape meet.
The word's original, non-mathematical sense — the highest point of the skull, or the topmost point of anything — has faded almost entirely from everyday use, meaning nearly all modern use of "vertex/vertices" is technical, concentrated in geometry, computer graphics, and anatomy, which likely explains why the classical plural has faced essentially no pressure to regularize the way more everyday Latin borrowings have. In computer graphics specifically, "vertex" and "vertices" have become such foundational technical vocabulary that graphics programming courses introduce the term extremely early, often before students encounter any other Latin-plural vocabulary at all, meaning many programmers absorb "vertices" as a purely technical term with little awareness of its broader classical Latin origin or its connection to ordinary geometry class.
Usage note
"Vertexes" is listed in some dictionaries as an acceptable alternative, but it's rare enough in actual mathematical and technical writing that most specialists would find it noticeably unusual; "vertices" is close to the only plural a geometry student, architect, or graphics programmer will ever actually encounter.
"Vertical," the everyday adjective most speakers associate with "vertex," is fully regular and has drifted into extremely broad general use describing anything upright or up-and-down, far beyond the specific geometric meaning the noun itself retains — a common pattern where an adjective built on a technical Latin noun becomes ordinary vocabulary while the noun stays confined to its specialist field. Video-game development documentation almost universally uses "vertex count" as a fixed technical phrase describing how detailed a 3D model is, keeping "vertex" singular within that specific compound regardless of how many actual vertices the model contains, treating the phrase as a descriptive measurement term rather than as a literal count. Astronomy occasionally borrows the term to describe the point from which a meteor shower appears to radiate, a niche but genuine extension of the geometric sense into observational astronomy.
Common real mistakes
Because "vertex" and "vortex" (a rotating mass of fluid or air) look and sound similar and share a related Latin root, writers occasionally confuse the two words entirely, though their plurals follow the identical -ex/-ices pattern regardless ("vortices" for "vortex"), so the confusion is about meaning, not about which plural pattern applies. A further point of confusion some beginners encounter: mistaking "vertex" for "vortex" in casual conversation despite the two words having entirely different meanings, an error of vocabulary rather than of grammar, though both words happen to share the identical Latin -ex/-ices plural pattern regardless.
The wider pattern
"Vertex/vertices" shares its Latin -ex/-ices pattern with "index/indices," "apex/apices," and "codex/codices," a family concentrated almost entirely in mathematics, computing, and formal technical writing where the classical plural remains dominant and largely unchallenged.
Examples
- The triangle has three vertices, one at each corner.
- Each vertex of the polygon was labeled with a letter.
- The graphics engine renders thousands of vertices every frame.
- A cube has eight vertices and twelve edges.
- Engineers marked the vertices of the structural frame precisely.
- The software connects each pair of vertices with a straight line.
- Two vertices of the shape overlapped, creating a rendering error.
- Architects calculated stress at every vertex of the dome.
- The 3D model's vertices were adjusted to smooth the surface.
- Each vertex in the network graph represented a different city.
- The polygon's vertices were recalculated after the model was rotated.
- A parabola's vertex marks either its highest or lowest point.
- The engineer double-checked each vertex before finalizing the bridge design.