Does anyone know why they always seem to end in "a"?

Samantha
Endora
Tabatha
Aunt Clara
Esmeralda
Aunt Hagatha

And it's not just a Bewitched thing. Remember Sabrina, the Teenage Witch? And the two witches from The Wizard of Oz/Wicked: Glinda and Elphaba?

I figured out once that the only witch whose name didn't end in an "A", was Mary. When we are first introduced to Aunt Clara, in episode 7, "The Witches are Out", Clara was with 2 other witches Bertha and Mary.

Some others:

Serena
Enchantra
Carlotta