In Greek grammar, it is also called the alpha declension, since its forms have the letter α, at least in the plural.
Therefore, it is assumed to be a newer formation: a suffix based on the neuter plural ending *-(e)h₂, forming a collective noun.
Greek first declension has two basic classes of feminine endings and one basic class of masculine endings, distinguished by their original nominative singular: long -ā, short -(y)ă, long -ās.
By contrast, other dialects tend to generalize the vowel one way or the other — Ionic has only ē, and Doric and Aeolic have only ā.
Here are examples of this class, which is complex because of sound changes involving the y (see Ancient Greek nouns: short a):