Peg

I've heard of families calling their daughters Peg (for Margaret), because it was tradition to name girls after their mothers. Therefore there would be several Margarets in one family- and several nicknames to differentiate- Maggie, Meg, Peg, Peggy. Since we don't pass on names like that any more, Peg sounds a little odd and outdated.

I get why this name comes from Margaret. Peg rhymes with Meg, and Meg is a short form of Margaret.