Polly is a variant of Molly, itself a diminutive of Mary. The reason for the change in spelling is that in the Middle Ages Ps were commonly exchanged for Ms in nicknames. Later on, Polly bacame a name of its own right. It's the name of a song by Nirvana, as well as a play by John Gay. Mary is an English form of Maria, the name used in the New Testament, ultimately derived from the Hebrew name Miryam. There are several possible meanings of Miryam, some of them being: "lots of bitterness", "wished for child", "bitter", "rebellious". Mary is the name of different characters in New Testament, the most important ones being the Virgin Mary, mother of Jesus, and Mary Magdalene. The name has been extremely popular for centuries, especially among Christians.