Foreign nouns form their foreign plural by changing their endings as follows:
1. "is" changes to "es".
2. "um" changes to "a".
3. "us" changes to "i".
4. "a" changes to "ae".
5. "on" changes to "a".
6. "x" changes to "ces".
7. "eau" adds "x."
Example: analysis, analyses.
Example: datum, data.
Example: alumnus, alumni, (masculine)
Example: alumna, alumnae, (feminine)
Example: criterion, criteria.
Example: index, indices.
Example: bureau, bureaux.
In a number of instances, however, the English plurals are commonly used instead of the foreign plurals.
Examples:
SINGULAR PLURAL
formula formulas
memorandum memorandums
index indexes
referendum referendums
bureau bureaus
tableau tableau s
trousseau trousseau s
