Plural form of words ending in -us
English borrowings from Latin and Greek
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).
“Plural form of words ending in -us” enters the record as english borrowings from Latin and Greek. Crown Archives preserves that source wording while asking what Plural, form and words can confirm, complicate or overturn.
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This entry incorporates text from “Plural form of words ending in -us” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.