In this lesson, you’ll learn how to avoid making common mistakes with Latin plural endings. These irregular words have different singular and plural forms in English, which are important for you to know and use correctly so that you make an intelligent impression. Watch the video to find out whether it’s fungi or funguses? Criteria or criterion? And when to use phenomena or phenomenon…

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English Common Mistakes: Latin Plural Endings

Most English nouns take –s, –es or -ies for their plural form.
▪ dog / dogs
▪ bus / buses
▪ baby / babies

Words with Latin plurals are the exception. These academic and scientific words retain their original Latin singular and plural endings. Since Latin isn’t widely taught nowadays, words with Latin plurals are often used incorrectly in English. Common mistakes include:

  1. Getting the singular and plural forms of the noun mixed up.
  2. Incorrectly adding an –s to a word that is already plural, e.g. ‘Here are the datas.’
  3. Incorrectly adding -es to make a plural, e.g. ‘funguses.’ ⬅ ❌

Note: The word ‘data’ is technically a plural noun. However, the meaning is often used in the singular, which is acceptable, because few people know or use the singular form ‘datum’. Therefore, both of the sentences below are correct:
🟡 Here is the data.
🟡 Here are the data.

1. fungus vs fungi

These words are scientific terms for mushrooms.

Singular form: fungus

Plural form: fungi

Common mistake: funguses

2. cactus vs cacti

Singular form: cactus
A spiky plant found in the desert!

Plural form: cacti
Pronounce it like a tie you wear around your neck ➡ ‘KAK-tie‘.

Common mistake: cactuses

3. crisis vs crises

Singular form: crisis
A crisis is a difficult period in your life where something shocking or unexpected happens. Pronounce it using the word ‘cry’ joined with the first syllable of the word sister: ‘sis’.

Plural form: crises
Pronounce this using the word ‘cry’ again, but this time joined with the word ‘seas’ (like the ocean)CRY-seas.

Common mistake: crisises

4. criterion vs criteria

Singular form: criterion
The meaning of this word goes back to the word ‘critic’ in ancient Greek, which means ‘to judge something’. Therefore, the word criterion means a single factor by which something is judged.

Plural form: criteria
Then we have a set of criteria, these are the rules or requirements by which something is judged. For example, ‘To apply for this job, you need to meet the selection criteria’ (more than one requirement must be met).

Common mistakes: criterions or criterias

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5. phenomenon vs phenomena

Singular form: phenomenon
The meaning of this word is to do with something that is observable in a scientific sense; we could be talking about the weather, the social sciences, or something that has changed from its natural behavior. For example, more people than ever are working from home so we could say: ‘Working from home is a recent social phenomenon’.

Plural form: phenomena

Common mistake: phenomenons

Pronunciation Note: The <ph> spelling at the start of both of these words is pronounced as an /f/ sound.

6. datum vs data

Singular form (rarely used): datum

Plural form: data
This is a word to describe information that is collected.

Common mistake: datas

7. memorandum vs memoranda

Singular form (very formal): memorandum
This word means ‘an official notice’. It tends to be used in formal or legal contexts. For example, when buying a house, the ‘memorandum of sale’ is a document that contains the essential details of the transaction.

Plural form (very formal and rarely used): memoranda
Example: ‘The bank will send out information memoranda to potential investors next week’.

Shortened: memo (singular) or memos (plural)
“Did you get the company memo?”

Common mistakes: memorandas or memorandums

8. medium or media?

This pair of words is unusual because the singular and plural meanings are different.

Singular form: medium
The word ‘medium’ is used to refer to the material that was used to create an artwork. If you go into an art gallery and read the description under the picture that you’re looking at, you’ll see that the medium used to create it is pastel on paper, for example. In occasional circumstances, it is possible to use the word ‘mediums’, such as in this example sentence: ‘Painting, sculpture and drawing are the traditional mediums of art’.

Plural form: media
Media’ is the word that we use to refer to the newspapers, television channels, or the radio – all different forms of news. It is always incorrect to say ‘the news medias’. Instead, we must say, ‘The issue has been widely discussed in the media’ (here ‘media’ means television, newspapers, radio etc.).


Don’t pronounce these plural words with an -s or -es on the end:

  • funguses
  • cactuses
  • criterions
  • phenomenons
  • datas
  • memorandas
  • medias

Lesson Roundup

Thank you for joining me for this lesson and for removing some common mistakes with Latin singular and plural endings from your English.

Extend Your Learning

▶︎ Download the lesson worksheet, which contains extra notes on pronunciation and sentence examples: Latin Plurals Worksheet.

▶︎ Watch another common English mistakes lesson on ‘inquiry’, ‘query’ and ‘enquire’.

▶︎ Learn the difference between confusing phrasal verbs ‘Go back’ VS ‘come back’


Jade Joddle grows your confidence and skill to shine when speaking English.

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