-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.