English plurals are usually easy to form. We can add -s to the end of the singular word, e.g.: chair (singular) or two chairs (plural). But, like almost all of the rules in English grammar, there are exceptions for the plural form of some nouns. Here is a list of the confusing singular/plural words.
Criterion & Criteria
‘Criterion’ is singular form and ‘criteria’ is plural form.
Meaning: a rule or principal used in evaluation.
“One criterion for grading this essay will be announced.”
“What were the criteria used to choose the winner?”
Phenomenon & Phenomena
‘Phenomenon’ is singular form and ‘phenomena’ is plural form.
Meaning: an observable fact or event.
“Star Wars eventually became a cultural phenomenon.”
“Lightning and earthquakes are natural phenomena.”
Datum & Data
‘Datum’ is singular form and ‘data’ is plural form.
Meaning: a single piece of information
“The datum shows little without the rest of the statistics.”
“The data were collected over a period of three months.”
Stratum & strata
‘Stratum’ is singular form and ‘strata’ is plural form.
Meaning: a level or class to which people are assigned according to their social status, education, or income.
“Discrimination exist in every stratum of society.”
“Different social strata are most likely crashing into each other.”
Bacterium & bacteria
‘Bacterium’ is singular form and ‘bacteria’ is plural form.
Meaning: a type of unicellular microorganism that are important to human because of their chemical activities but some of its type often cause disease.
“Every bacterium is prokaryotic.”
“Tetanus is a serious ilness caused by Clostridium tetani bacteria.”
- Merriam-Webster Dictionary