Plural of Datum
“Datum” is a specialized singular noun meaning one item or piece of data, and its traditional plural is “data.” Modern usage has also developed “data” as a mass/uncount noun, so agreement with “data” varies by context and editorial convention.
The traditional plural of “datum” is “data.” In modern English, however, “data” is also widely treated as an uncount noun that can take singular agreement, especially outside highly formal or technical contexts.
Key details
Choose the right form
| Meaning / situation | Form / construction | Decision |
|---|---|---|
| one discrete item in a context that uses the technical singular | datum | Use “datum” when the singular is genuinely needed. |
| traditional plural of datum | data | Use “data” for multiple items under the traditional count pattern. |
| modern mass/uncount treatment | data | Agreement can be singular in established modern usage; follow field or house style. |
Quick tests
Meaning / construction test
Are you distinguishing one technical item from multiple items under the traditional count pattern?
If yes: Use “datum” for one and “data” for more than one.
If no: If “data” is being used as a modern mass noun, follow the grammar and style convention of the context rather than forcing “datum.”
Caveat: The inflectional history and modern agreement pattern are separate questions: “datum” → “data” remains the traditional number contrast, while “data” can also function as a mass noun.
Examples
One datum was excluded from the calculation.
“Datum” is the specialized singular for one item.
These data were collected in two stages.
This sentence uses the traditional plural treatment of “data.”
The data is stored locally.
Modern English also allows mass-noun “data” with singular agreement in contexts that adopt that convention.
Further guidance
Core difference
The inflection is “datum” → “data,” but modern “data” can also function as an uncount noun.
Fast Test
Use “datum” when you genuinely mean one discrete item in a context that uses the term. For multiple items, “data” is the traditional plural; follow the governing style or field for singular versus plural agreement with “data.”
Usage Boundary
Do not force “datum” into ordinary prose merely to create a singular for “data.” The singular survives mainly in specialized contexts, while mass-noun “data” is established in modern usage.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- Datum — Cambridge Dictionary (opens in a new tab)Cambridge University Press · Direct lexical evidence that datum is a specialized singular noun whose plural is data.
- Data — Cambridge Dictionary (opens in a new tab)Cambridge University Press · Direct usage evidence that data historically functions as the plural of datum and is also widely used as an uncount noun with singular agreement.