English pluralswikipedia
English nouns are inflected for grammatical number, meaning that if they are of the countable type, they generally have different forms for singular and plural.
pluralpluralsback-formedderived from the Frenchregular nounidentical in the singular and pluralplural in form but usually singular in constructionFrench compoundsEnglish plural noun formdefective

Inflection

inflectioninflectedinflectional morphology
English nouns are inflected for grammatical number, meaning that if they are of the countable type, they generally have different forms for singular and plural.
For details, see English plural, English verbs, and English irregular verbs.

English grammar

Englishgrammarthere is
English nouns are inflected for grammatical number, meaning that if they are of the countable type, they generally have different forms for singular and plural.
For more details, see English plural.

Morpheme

morphememorphemesmorphemic
The plural morpheme in English is suffixed to the end of most nouns.
For example, in English, the plural marker -(e)s of regular nouns can be pronounced (bats), (bugs), or, (buses), depending on the final sound of the noun's plural form.

Consonant voicing and devoicing

devoicingvoicingdevoiced
In Old and Middle English voiceless fricatives, mutated to voiced fricatives before a voiced ending.
English no longer has a productive process of voicing stem-final fricatives when forming noun-verb pairs or plural nouns, but there are still examples of voicing from earlier in the history of English:

Plural

pluralpl.pl
English nouns are inflected for grammatical number, meaning that if they are of the countable type, they generally have different forms for singular and plural.
(For details and different cases, see English plural).

Zero (linguistics)

zeroØ
Some nouns have identical singular and plural (zero inflection).

Old English

Old EnglishAnglo-SaxonSaxon
The modern English plural ending -(e)s derives from the Old English -as, but the latter applied only to "strong" masculine nouns in the nominative and accusative cases; different plural endings were used in other instances.

Back-formation

back-formationback formationback-formed
In the American fashion industry it is common to refer to a single pair of pants as a pant —though this is a back-formation, the English word (deriving from the French pantalon) was originally singular.
Many words came into English by this route: Pease was once a mass noun but was reinterpreted as a plural, leading to the back-formation pea.

English words of Greek origin

Greekwords that have been borrowed from GreekGreekfor upsilon in Greek loan-words
Some Greek plurals are preserved in English (cf. Plurals of words of Greek origin):
And there are misleading cases: pentagon comes from Greek pentagonon, so its plural cannot be *pentaga; it is pentagons (Greek πεντάγωνα/pentagona) (cf. Plurals from Latin and Greek).

English verbs

-edEnglishEnglish regular verbs
These are the same rules that apply to the pronunciation of the regular noun plural suffix -[e]s and the possessive -'s.

Biceps

bicepsbiceps brachiibiceps brachii muscle
The term, from Latin, for the main upper arm flexor in the singular is the biceps muscle (from biceps brachii); however, many English speakers take it to be a plural and refer to the muscle of only one arm, by back-formation, as a bicep.
The English form, attested from 1939, is a back formation derived from interpreting the s of biceps as the English plural marker -s.

Postpositive adjective

postpositive adjectivepost-positive adjectivePost-positive
These heads are also nouns and the head usually pluralizes, leaving the second, usually a post-positive adjective, term unchanged:
In the plural forms of expressions with postpositive adjectives or other postpositive modifiers, the pluralizing morpheme (most commonly the suffix -s or -es) is added after the noun, rather than after the entire phrase.

Plurale tantum

plurale tantumpluralia tantumplural
Such a noun is called a plurale tantum.

Toyota Prius

PriusPrius EcoToyota Prius apr GT
In February 2011, Toyota USA asked the US public to decide on what the most proper plural form of Prius should be, with choices including Prien, Prii, Prium, Prius, or Priuses.

Ox

oxoxenbullock
An ox (plural oxen), also known as a bullock in Australia and India, is a bovine trained as a draft animal or riding animal.

Pigs in a blanket

pigs in a blanketpigs in blanketssmall cocktail frankfurters
Pigs in a blanket (defective, also pig in a blanket) is a variety of different sausage-based foods in the United States, United Kingdom, Denmark, Republic of Ireland, Germany, Belgium, Russia, Canada, and Japan.

Barracks

barracksbarrackmilitary barracks
The word may apply to separate housing blocks or to complete complexes, and the plural form often refers to a single structure and may be singular in construction.

Formula

formulamathematical formulaformulas
The plural of formula can be spelled either as formulas (from the most common English plural noun form) or, under the influence of scientific Latin, formulae (from the original Latin).

Aurochs

aurochsBos primigeniuswild ox
The word is invariable in number in English, though sometimes a back-formed singular auroch and/or innovated plural aurochses occur.

Hippopotamus

hippopotamushippohippos
In English, the plural is "hippopotamuses", but "hippopotami" is also used; "hippos" can be used as a short plural.

A Dictionary of Modern English Usage

FowlerModern English UsageFowler's Modern English Usage
Covering topics such as plurals and literary technique, distinctions among like words (homonyms and synonyms), and the use of foreign terms, the dictionary became the standard for other guides to writing in English.

Pound sterling

£pound sterlingpounds sterling
The full official name pound sterling (plural: pounds sterling), is used mainly in formal contexts and also when it is necessary to distinguish the United Kingdom currency from other currencies with the same name.

Bateau

bateaubateauxbatteau
The name derives from the French word, bateau, which is simply the word for boat and the plural, bateaux, follows the French, an unusual construction for an English plural.

Cumulativity (linguistics)

cumulativitycumulative reference
The plural form "houses", however, does have cumulative reference.

Pokémon

Pokémon'' franchisePokémongeneration
"Pokémon" is identical in the singular and plural, as is each individual species name; it is grammatically correct to say "one Pokémon" and "many Pokémon", as well as "one Pikachu" and "many Pikachu".