The noun vertex has two meanings: (1) the highest point, and (2) the point at which the sides of an angle intersect. Vortex means a whirling mass of matter. Both are often used metaphorically—vertex for the meeting point between two or more things, and vortex for any chaotic, figuratively swirling mass.
Though the words have no definitions in common, they’re both derived from the Latin vertere, meaning to turn. Each is pluralized in a pair of ways—vertexes/vertices, and vortexes/vortices. Each word’s -ices version is more common than the -exes version.
Examples
Because they’re similar in sound and both relatively rare, vertex and vortex are easy to confuse—for example:
A third chair, making the vortex of a triangle between the president and the ambassador, was occupied by a female translator from the State Department. [Treason, by Don Brown]
A gigantic, gaping, swirling vertex appeared, with the sludge in the very center. [The Neopian Times]
And these writers use vertex and vortex correctly:
The point where the arcs intersect marks the third vertex of your equilateral triangle. [Science Magazine]
A boat was caught in the vortex of a whirlpool at sea. [Winnipeg Free Press]
Imagine a triangle with Student, Teacher, and Subject at the vertices. [The Times Record]
Rather, it repeatedly flings its wings forward to create tiny vortices of pressurized air. [Popular Science]
