data
Although data is the plural of Latin datum, it is commonly used in English as singular.
In formal academic language, however, data is still often plural:
The data are inconclusive.
criteria
Criteria is the plural of criterion:
Singular
The sole criterion in the selection process was …
Plural
Many criteria were used in the selection process.
phenomena
Phenomena is the plural of phenomenon:
Singular
This phenomenon can be seen in …
Plural
Several different phenomena can be observed …
media
Media is the plural of medium:
Singular
The internet is a new and exciting medium.
Plural
The media are often blamed for society’s ills.
bacteria
Bacteria is the plural of bacterium:
Singular
A single bacterium is too small to be seen with the naked eye.
Plural
While some bacteria are harmful, others are beneficial.
strata
Strata is the plural of stratum:
Singular
Each stratum represents a different period.
Plural
Sequences of sedimentary strata