-a²

Also ‑ata.

The plural of certain nouns of Latin or Greek origin.

From the Latin or Greek neuter plural ending.

Many nouns from Latin or Greek that end in ‑um or ‑on form their plurals in ‑a, as for example datum changes to data and phenomenon to phenomena. Such plurals are now often formed using ‑s instead.

A further group, mostly specialist words, whose singulars already end in ‑a, can form their plurals in ‑ata. Examples are lemma (plural lemmata), schema (schemata), stigma (stigmata), and trauma (traumata). Here, too, plurals in ‑s are now common.

The same plural form occurs in the scientific names of many classes of animals, such as Mammalia, Amphibia, Cetacea, Crustacea, Mollusca, and Protozoa (see also ‑acea and ‑ia).