Plural of “apex”

The plural of apex is apices (some dictionaries also accept apexes).

Why

"Apex" is Latin for "tip" or "summit," a third-declension noun whose classical plural was "apices." English borrowed the word largely intact in the 17th century for geometry and anatomy, contexts that historically favored keeping the Latin plural — a triangle's apices, a lung's apices in medical anatomy.

Outside those specialist fields, though, "apexes" has become the clearly dominant plural in modern general English, especially in figurative use ("the apexes of their careers," race-driving's "apex" of a turn). Style guides and most dictionaries now list "apexes" first or as equally standard, a genuine shift from a century ago when "apices" was treated as the only correct form.

Usage note

Choose based on register and audience: anatomy and formal geometry writing still lean toward "apices," while sports, business, and everyday figurative writing overwhelmingly use "apexes." Neither is wrong, but "apexes" reads as the unmarked, natural choice for most general audiences today.

Auto racing has given the word a specific technical sense — the apex of a curve, the innermost point a driver's line touches — and racing commentary almost always says "apexes," not "apices," when discussing multiple corners, showing how a word's plural can regularize faster within a newer specialist community than within an older one. The word's biological use has grown too — "apex predator," describing an animal at the top of a food chain with no natural predators of its own, has become common enough in nature documentaries and ecology writing that its plural, "apex predators" (not pluralizing "apex" alone but as part of the compound), rarely needs to distinguish between "apices" and "apexes" at all, since the phrase functions almost as a fixed compound term.

Common real mistakes

Some writers mistakenly pluralize "apex" as "apexs," dropping the necessary -e before the -s; a sibilant ending like this one calls for either the full "-es" or the Latin "-ices," but never a bare -s tacked directly on.

The wider pattern

"Apex" sits in the middle of the Latin -ex spectrum: unlike "annex" (Latin plural never used in English) or "vortex" (Latin plural still dominant in its technical field), "apex" shows the Latin and regularized plurals in genuine, ongoing competition across different registers of the same word. In business writing specifically, "the apex of the market" and similar phrases describing peak points in an industry or cycle have become common enough that some style guides now list "apexes" as the default plural for business and financial writing entirely, treating "apices" as reserved almost exclusively for anatomy and pure geometry.

Examples

• The two apices of the triangle were marked in red on the diagram.
• Doctors examined both apices of the patient's lungs on the scan.
• Her retirement marked one of the true apexes of a long career.
• The driver hit both apexes of the chicane perfectly on that lap.
• Historians point to several apexes in the empire's long, uneven decline.
• The mountain range has three apices visible from the valley floor.
• Reviewers called the film one of the apexes of the director's career.
• The survey recorded the apices of each roof truss for the engineers.
• Analysts identified two separate apexes in the company's stock history.
• The gymnast's routine included two apexes of difficulty back to back.
• Wolves and sharks are both considered apex predators in their respective habitats.
• The negotiations reached one of several apexes before finally collapsing.
• Climbers marked the apexes of both peaks on their trail map.
• The season's apexes in ratings came during the two finale episodes.
• Analysts marked two apexes in the stock's volatile five-year history.
• The trail guide identified the apexes of both nearby peaks.
• Her career reached new apexes after the surprising promotion.
• The bridge design required precise calculations at both structural apexes.