What does Cynthia mean?
Cynthia is from Greek Kynthia, an epithet of Artemis meaning 'from Mount Cynthus,' her birthplace on Delos. The moon association comes because Artemis (and Selene) were called Cynthia; it is cultural, not a literal 'moon' etymology.
What does Margaret mean?
Margaret comes from the Greek margaritēs, “pearl.” Borne by saints and by queens across Europe, it has generated an unusually rich crop of nicknames, from Maggie and Meg to Peggy and Greta.