English is full of quirks, and one of the trickiest involves words we almost always hear in plural form, even though they have perfectly good singular versions. This can lead to awkward grammar mistakes, especially in writing.

Below are nine commonly misused plural nouns, their singular forms, and how to use them correctly in sentences.

1. Data

Singular: Datum
Correct: The data show that the drug effectively lowers cholesterol.
Tip: Use a plural verb with “data” unless you’re in a highly technical or scientific setting using “datum.”

2. Criteria

Singular: Criterion
Correct: The most important criterion for selection is leadership potential.
Note: “Criteria” is plural—avoid saying “a criterion.”

3. Media

Singular: Medium
Correct: The media are often accused of being biased.
Clarify: Use “medium” when referring to a single form, like “TV is a powerful medium.”

4. Alumni

Singular: Alumnus (male), Alumna (female); Alumnae (female plural)
Correct: The alumni gathered for their 10-year reunion.
Pro tip: Use “alum” as a gender-neutral alternative in casual settings.

5. Dice

Singular: Die
Correct: Yahtzee is played by rolling five dice.
Fun fact: Most people never say “die” unless they’re playing a board game.

6. Bacteria

Singular: Bacterium
Correct: A single bacterium can multiply rapidly in the right conditions.
Scientific note: In casual speech, “bacteria” is often treated as singular, but it’s still grammatically plural.

7. Algae

Singular: Alga
Correct: Some species of algae are used in cosmetics and food supplements.
Usage tip: You’ll most often encounter this in biology or environmental discussions.

8. Paparazzi

Singular: Paparazzo (male), Paparazza (female – rare)
Correct: The paparazzi swarmed the red carpet.
Media insight: “Paparazzi” is now widely used even when referring to just one person.

9. Parentheses

Singular: Parenthesis

Correct: The sentence includes a confusing parenthesis.
Grammar tip: Parentheses are punctuation marks; a parenthesis is the actual aside or clause inside them.

Final Tip:

These singular forms may sound unusual, but using them correctly can boost your credibility, especially in academic, professional, or editorial settings.