Nebula, gymnasium, hypothesis — do you know how to make these plural? English is famous for borrowing words from other languages, but the rules don’t always follow the original root languages. Many nouns in English have roots in Latin and Greek, and when it comes to turning those words into plurals, the rules can get a little tricky.
Latin and Greek Rules
The rules for making Greek- and Latin-origin nouns plural come directly from the root languages, but learning the full languages isn't required.
For nouns ending in “-a,” switch the final letter to “-ae” to make the word plural.
alga → algae
larva → larvae
vertebra → vertebrae
Nouns with an “-um” ending turn into an “-a” ending.
candelabrum → candelabra
medium → media
spectrum → spectra
Words that end in “-is” are swapped to “-es” to make them plural.
paralysis → paralyses
diagnosis → diagnoses
thesis → theses
Terms that end in “-us” can be made plural using “-i” in place of “-us.”
cactus → cacti
alumnus → alumni
syllabus → syllabi
Plurals Don’t Always Follow Rules
Many of these Greek- and Latin-origin words follow traditional plural rules, but in English, rules are meant to be broken.
Take the word “hippopotamus.” Because it has the “-us” ending, the correct plural form should be “hippopotami.” But according to most dictionaries, “hippopotamuses” is also acceptable.
As English evolves, more standard “-s” or “-es” endings have been adopted for many Greek and Latin plurals. Consider which of these plurals looks correct to you. The accepted plural is bolded.
aquarium / aquaria / aquariums
podium / podia / podiums
formula / formulae / formulas
bureau / bureaux / bureaus
index / indices / indexes
Often, the traditional Greek or Latin ending is used in more formal contexts like academic or scientific writing. “Indices” is still likely to be used in technical writing. A scientist describing her findings at a professional conference might use words like “vortices” and “radii.” But two friends discussing the weather forecast would be more likely to speak of “vortexes” and “radiuses.”
Plurals Gone Wild
One final note: Some nouns with Greek and Latin roots have plural forms that have become so widely used they have eclipsed the singular counterparts.
agendum → agenda
criterion → criteria
bacterium → bacteria
datum → data
When was the last time you used the singular form of any of these words?
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