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English Latin words

Words in English You Probably Didn’t Realize are Latin

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Dalia Y

BA, MA, Phil. Grammarflex's initial initiator and contributor.




What’s the plural of “deer”

Aside from cliché phrases like carpe diem (“seize the day”), or shortened forms like i.e. and e.g., (which, by the way, are very common in English), there are also regular words and nouns which follow distinct Latinate patterns.

Understanding Latin Words in Modern English

Latin noun patterns in English

Nouns in English that use their original Latinate forms are trickier for English speakers (and learners) to remember because they don’t follow typical English plural noun rules. Most nouns in English simply add ‘s’ or ‘es’ to denote a plural (e.g., dog/dogs, table/tables).

Latin nouns, however, use their own singular and plural endings, of which there are a few notable patterns. We can remember their correct singular and plural forms by recognizing the suffixes these nouns use.

Common Latin Word Patterns

Words ending in “-ex” / “-ix” to “-ices”

A common singular noun ending is “-ix” and “-ex”, which converts to “-ices” as a plural.
Singular Plural
matrix matrices, matrixes
vortex vortices, vortexes
vertex vertices, vertexes
index indices, indexes
appendix appendices, appendixes
apex apices, apexes
codex codices, codexes

Words ending in “-us” / “-i”

Same as the group of words above, these nouns have also come to use a standard English noun form as well (in addition to their original Latin forms).

Though, by and large, most nouns that are Latin and end in “-us” will switch to “-i” as a plural. However, this is not invariably true, since words like “virus”, “platypus” and even “octopus” now reluctantly use the “-i” ending as a plural (platypus and octopus both being originally Greek). We would not, however, say “viri” as a plural for “virus” (it’s just viruses).

Singular Plural
cactus cacti, cactuses
syllabus syllabi, syllabuses
alumnus alumni, alumnus’s
fungus fungi, funguses
radius radi, radiuses
stimulus stimuli, stimuluses
nucleus nuclei, nucleuses
hippopotamus hippopotami, hippopotamuses

Words ending in “-on” / “-um” to “-a”

Interestingly, words like “media”, “criteria” and “bacteria” are all plural forms, which are for the most part used exclusively (relative to their singular noun counterparts). It’s uncommon to hear “bacterium” or “datum”, except perhaps in scientific or academic writing.

Also, like the previous groups, these words likewise retain their original Latin form but have also come to accept an English standard form as well.

Singular Plural
phenomenon phenomena, phenomenons
criterion criteria
bacterium bacteria
datum data
medium media
addendum addenda, addendums
colloquium colloquia, colloquiums
referendum referenda, referendums
memorandum memoranda, memorandums
curriculum curricula, curriculums
erratum errata, erratums
symposium symposia, symposiums
stratum strata, stratums
spectrum spectra, spectrums

Words ending in “-a” / “-ae”

Singular Plural
formula formulae, formulas
vertebra vertebrae, vertebras
larva larvae, larvas
nebula nebulae, nebulas
antenna antennae, antennas

“Antenna” prefers antennae as a plural to refer to an insect appendage, and antennas to refer to a television’s antenna

Summary of Latin Word Patterns

Singular Plural
formula formulae, formulas
vertebra vertebrae, vertebras
larva larvae, larvas
nebula nebulae, nebulas
antenna antennae, antennas

“Antenna” prefers antennae as a plural to refer to an insect appendage, and antennas to refer to a television’s antenna.

Summary of Latin Word Patterns

Pattern Singular Plural Example
-ix/-ex to -ices matrix matrices index → indices
-us to -i cactus cacti alumnus → alumni
-um/-on to -a datum data phenomenon → phenomena
-a to -ae formula formulae nebula → nebulae
💡Study Tip

When in doubt about Latin plurals, both the traditional Latin form and the English “-s/-es” form are often acceptable in modern usage.

Worksheet: Latin nouns

Question 1 of 10

According to its Latin pattern, what is a common plural form of “matrix”?



Which is the Latin plural form for a group of male or mixed-gender graduates?



Based on the blog post, which of these words is often used in its plural form in modern English?



Following the Latin pattern, what is the plural of “radius”?



Which word is the singular form of “criteria”?



The researchers collected important for their study.



She proudly joined the of her university after graduation.



The story was covered across all types of .



You must meet all of these to pass the course.



The first for selection is previous experience.





FAQs

Why don't Latin words follow English rules?
+

Latin nouns often keep their original singular and plural endings instead of just adding 's' or 'es', making them different from typical English nouns discussed in the post.

What's the plural of words like "index"?
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Words ending in "-ex" or "&text{–}ix" typically form the plural by changing to "-ices," like "index" becoming "indices" or "appendix" becoming "appendices." English forms like "indexes" are also used.

What's the rule for words like "cactus"?
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Nouns ending in "-us" usually change to "-i" for the plural, such as "cactus" becoming "cacti" or "alumnus" becoming "alumni." English plurals like "cactuses" are also accepted.

What about words ending in "-um"?
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Words ending in "-um" typically change to "-a" for the plural, like "datum" becoming "data" or "medium" becoming "media." English plurals are also accepted for some like "addendums."

Are words like "media" singular or plural?
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Words like "media" and "criteria," originally Latin plurals from "-um" and "-on" endings, are often used exclusively as plurals in common English usage mentioned in the post.

"Yash,. ""Words." "Grammarflex", Jun 25, 2025, .

Sources

  1. Oxford English Dictionary. “Latin plurals in English.” Oxford University Press.


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