Some nouns of Latin and Greek origin have kept their own plural endings. The plural ending “es” as in the word “analyses” is pronounced [i:z], the ending “i” as in the word “alumni” is pronounced [ai], the ending “ae” as in “vertebrae” is pronounced [i:]. Nouns with Latin and Greek plural endings are divided here into groups according to the ending.

The English plural ending s/es is also used with some of these nouns; in such cases, two variants are given, and the variant with the English ending s/es is marked with the letter (E). In a few cases, English and Latin plural forms are not interchangeable, for example: radio antennas, an insect’s antennae; mass media (radio, TV, newspapers), spiritualistic mediums (people regarded as mediums).

Group 1

analysis – analyses

axis – axes

basis – bases

crisis – crises

diagnosis – diagnoses

hypothesis – hypotheses

oasis – oases

parenthesis – parentheses

thesis – theses

Group 2

abacus – abacuses (E), abaci

alumnus – alumni

apparatus – apparatus, apparatuses (E)

cactus – cactuses (E), cacti

calculus – calculi, calculuses (E)

corpus – corpora

focus – focuses (E), foci

fungus – fungi

genus – genera, genuses (E)

genius – geniuses (men of talent), genii (spirits)

hippopotamus – hippopotamuses (E), hippopotami

nucleus – nuclei, nucleuses (E)

octopus – octopuses (E), octopi

papyrus – papyri

radius – radii, radiuses (E)

rhombus – rhombuses (E), rhombi

stimulus – stimuli

stylus – styli, styluses (E); (

syllabus – syllabuses (E), syllabi

terminus – termini, terminuses (E)

Group 3

automaton – automatons (E), automata

criterion – criteria

phenomenon – phenomena

Group 4

addendum – addenda

bacterium – bacteria

curriculum – curriculums (E), curricula

datum – data

erratum – errata

forum – forums (E), fora

medium – media, mediums (E)

memorandum – memorandums (E), memoranda

millennium – millenniums (E), millennia

stadium – stadiums (E), stadia

stratum – strata, stratums (E)

Group 5

alumna – alumnae

antenna – (radio) antennas; b. antenna – (insects’) antennae

dogma – dogmas (E), dogmata

enigma – enigmas (E), enigmata

formula – formulas (E), formulae

stigma – stigmata, stigmas (E)

vertebra – vertebrae, vertebras (E)

Group 6

appendix – appendixes (E), appendices

matrix – matrices, matrixes (E)

apex – apexes (E), apices

index – indexes (E) (books), indices (maths)

vertex – vertexes (E), vertices

The tendency to use the foreign plural is still strong in the technical language of science, but in fiction and colloquial English there is an evident inclination to give to certain words the regular English plural in –s.

In compound nouns the plural is formed in different ways.

As a rule a compound noun forms the plural by adding –s to the head-word:

Editor-in-chief – editors-in-chief

Brother-in-law – brothers-in-law

Looker-on – lookers-on

In some compound nouns the final element takes the plural form:

lady-bird – lady-birds boy-friends

Forget-me-not – forget-me-nots travel agents

Merry-go-round – merry-go-rounds

Where man or woman is used in prefixes, both parts are made plural: men drivers, women drivers

Some nouns have only the plural form:

Trousers, spectacles, breeches, scissors, tongs, fetters, pants, slacks, tights, breeches, pyjamas, pliers, pincers, forceps. These are for the most part of names of things which imply plurality or consist of two or more parts. The word pantyhose is used in the singular.

There are nouns with the plural ending which are only in the plural: clothes, arms, goods, groceries, outskirts, troops, remains, savings, belongings.

Some uncountable nouns have the ending “s” in their form but are used only in the singular and with a singular verb, for example: news; names of games – billiards, cards, checkers, dominoes; names of diseases – measles, mumps. Names of scientific subjects are also singular: mathematics, physics, phonetics, linguistics, economics, politics, etc.

Initials can be made plural: MPs (members of Parliament), VIPs, OAPs (old age pensioners), UFOs.

Numerical expressions are usually singular, but can be plural if the individuals within a numerical group are acting individually:

Fifty thousand dollars is a lot of money.

One-half of the faculty is retiring this summer.

One-half of the faculty have doctorates.

Fifty percent of the students have voted already.

When a noun names the title of something or is a word being used as a word, it is singular whether the word takes a singular form or not.

Faces is the name of the new restaurant downtown.

Postcards is my favorite novel.

Plurals and Apostrophes. We use an apostrophe to create plural forms in two limited situations: for pluralized letters of the alphabet and when we are trying to create the plural form of a word that refers to the word itself. Here we also should italicize this “word as word,” but not the ‘s ending that belongs to it. Do not use the apostrophe + s to create the plural of acronyms (pronounceable abbreviations such as laser).

Jeffrey got four A’s on his last report.

You have fifteen and’s in that last paragraph.