Plural Form Of Words Ending In -us

In English, the plural form of words ending in ''-us'', especially those derived from Latin, often replaces ''-us'' with ''-i''. There are many exceptions, some because the word does not derive from Latin, and others due to custom (''e.g.'', ''campus'', plural ''campuses''). Conversely, some non-Latin words ending in ''-us'' and Latin words that did not have their Latin plurals with ''-i'' form their English plurals with ''-i'', ''e.g.'', ''octopi'' is sometimes used as a plural for octopus (the standard English plural is octopuses). Most Prescriptivists consider these forms incorrect, but descriptivists may simply describe them as a natural evolution of language; some prescriptivists do consider some such forms correct (e.g. ''octopi'' as the plural of ''octopus'' being analogous to ''polypi'' as the plural of ''polypus'').

Some English words of Latin origin do not commonly take the Latin plural, but rather the regular English plurals in -(e)s: ''campus'', ''bonus'', and ''anus''; while others regularly use the Latin forms: ''radius'' (''radii'') and ''alumnus'' (''alumni''). Still others may use either: ''corpus'' (''corpora'' or ''corpuses''), ''formula'' (''formulae'' in technical contexts, ''formulas'' otherwise), ''index'' (''indices'' mostly in technical contexts, ''indexes'' otherwise).

History

In Latin, most second declension masculine nouns ending in ''-us'' form their plural in ''-i''. However, some Latin nouns ending in ''-us'' are not second declension (''cf.'' Latin grammar). For example, third declension neuter nouns such as ''opus'' and ''corpus'' have plurals ''opera'' and ''corpora'', and fourth declension masculine and feminine nouns such as ''sinus'' and ''tribus'' have plurals ' and '.

Some English words derive from Latin idiosyncratically. For example, ''bus'' is a shortened form of '' omnibus'' 'for everyone', the ablative (and dative) plural of ''omnis'', and ''ignoramus'' is a verb form, 'we do not know'. ''Syllabus'' is a Late Latin (16th c.) word, derived from a misreading of the Greek ''sittybos'' "table of contents"; since it is not a classical word, some argue that it does not have a classical plural. However, the form ''syllabi'' is used and considered acceptable by some sources.

''Virus''

The English plural of ''virus'' is ''viruses''. In most speaking communities, this is non-controversial and speakers would not attempt to use the non-standard plural in -''i''. However, in computer enthusiast circles in the late 20th century and early 21st, the non-standard ''viri'' form (sometimes even ''virii'') was well attested, generally in the context of computer viruses. ''Viri'' is also found in some nineteenth-century sources.

While the number of users employing these non-standard plural forms of ''virus'' was always a small percentage of the English-speaking population, the variation was notable because it coincided with the growth of the web, a medium on which users of ''viri'' were over-represented. As the distribution of Internet users shifted to be more representative of the population as a whole during the 2000s, the non-standard forms saw decline in usage. A tendency towards prescriptivism in the computer enthusiast community, combined with the growing awareness that ''viri'' and ''virii'' are not etymologically supported plural forms, also played a part.

''Vīrus'' in Classical Latin was a mass noun, denoting something uncountable. These pluralize only under special circumstances, and no plural form of the word can be found in contemporary texts.

The Latin word ''vīrus'' was a neuter noun of the second declension, but neuter second declension nouns ending in ''-us'' (rather than ''-um'') are rare enough that inferring rules is difficult. (One rare attested plural, ''pelage'' as a plural of ''pelagus'', is borrowed from Greek, so does not give guidance for ''virus''.) Plural neuter nouns of other declensions always end in ''-a'' (in the nominative, accusative and vocative).

In Neo-Latin, a plural form is necessary in order to express the modern concept of 'viruses', leading to the following declension:

Usage of ''virii'' within Internet communities has met with some resistance, most notably by Tom Christiansen, a figure in the Perl community, who researched the issue and wrote what eventually became referred to in various online discussions as the authoritative essay on the subject, favoring ''viruses'' instead of ''virii''. The impetus of this discussion was the potential irony that the use of ''virii'' could be construed as a claim of superior knowledge of language when in fact more detailed research finds the native ''viruses'' is actually more appropriate. In other words, ''virii'' is a hypercorrection.

The form ''viruses'' appears in the official Scrabble words list, but neither ''viri'' nor ''virii'' does.

In life sciences, "viruses" generally refers to several distinct strains or species of virus. "Virus" is used in the original way as an uncountable mass noun, e.g. "a vial of virus". Individual, physical particles are called "virions" or "virus particles".

''Octopus''

There are three plural forms of ''octopus'': ''octopuses'', '' octopi'', and '' octopodes''. A fourth form ''octopods'' is occasionally used by scientists for taxonomic purposes.

Currently, ''octopuses'' is the most common form in the UK as well as the US; ''octopodes'' is rare, and ''octopi'' is often objected to as incorrect.

The ''Oxford English Dictionary'' lists ''octopi'', ''octopuses'' and ''octopodes'' (in that order); it labels ''octopodes'' "rare", and notes that ''octopi'' derives from the mistaken assumption that ' is a second declension Latin noun. (The long "ū" is not used in the 2nd declension.) Rather, it is (Latinized) Ancient Greek, from ' (, gender masculine), whose plural is ' ().

''Chambers 21st Century Dictionary'' and the ''Compact Oxford Dictionary'' list only ''octopuses'', although the latter notes that ''octopodes'' is "still occasionally used"; the British National Corpus has 29 instances of ''octopuses'', 11 of ''octopi'' and 4 of ''octopodes''. ''Merriam-Webster 11th Collegiate Dictionary'' lists ''octopuses'' and ''octopi'' (in that order); '' Webster's New World College Dictionary'' lists ''octopuses'', ''octopi'' and ''octopodes'' (in that order).

'' Fowler's Modern English Usage'' states that "the only acceptable plural in English is ''octopuses,''" and that ''octopi'' is misconceived and ''octopodes'' pedantic.

The term ''octopod'' (plural ''octopods'') is taken from the taxonomic order Octopoda but has no classical equivalent. The collective form ''octopus'' is usually reserved for animals consumed as food.

''Platypus''

The situation with the word '' platypus'' is similar to that of ''octopus''; the word is etymologically Greek despite its Latinized ending, and so pluralizing it as if it were Latin (i.e. as ''platypi'') is sometimes ill-considered. As with ''octopus'', importing Greek morphology into English would have ''platypodes'' as the plural, but in practice this form is hardly attested outside of discussions about pluralization. In scientific contexts, biologists often use ''platypus'' as both the singular and plural form of the word, in the tradition of ''sheep'' or ''fish'', but laypersons and scientists alike often use the simple English plural ''platypuses''. Different dictionaries make different recommendations.

Botanical Latin

As a word in Botanical Latin (as distinct from Classical Latin), ''cactus'' follows standard Latin rules for pluralization and becomes ''cacti'', which has become the prevalent usage in English. Regardless, ''cactus'' is popularly used as both singular and plural, and is cited as both singular and plural. ''Cactuses'' is also an acceptable plural in English.

Facetious formations

Facetious mock-erudite plurals in ''-i'' or even ''-ii'' are sometimes found for words ending with a sound (vaguely) similar to ''-us''. Examples are ''stewardi'' (supposed plural of '' stewardess'') and ''Elvi'' (as a plural for '' Elvis'' imitators). The Toyota corporation has determined that their ''Prius'' model should have the plural form ''Prii'', even though the Latin word ''prius'' has a plural ''priora'', the '' Lada Priora'' having prior claim to that name—though the common plural is "Priuses". Conversely, Toyota has also said that the plural of their ''Lexus'' line is ''Lexus''. The Winklevoss twins were famously referred to as "the Winklevi" in ''The'' ''Social Network''.Vanity Fair
"The Code of the Winklevi"
Dana Vachon, December 2011

References

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English grammar