Welcome to the Third Declension!
There are many nouns of masculine feminine and neuter gender that have this pattern.
Nominative a contracted form in the singular
A Plural – as ending
Accusative stem + α Plural – ας
Genitive + ος Plural ων
Dative + ι Plural σι(ν)
Nouns that end in – μα like Charisma Drama Dogma and Gramma are declined as
γραμμα γραμματα γραμματος γραμματων γραμματι γραμμασι
More Third Declension Examples soon.