Margaret is from the Greek 'Margarites', from 'margaron' a pearl, and ultimately, apparently, of Hebrew origin. The Greek word is also the source for 'margarine', since its inventor, van den Burgh, thought his initial product reminded him of pearls. The English have always been keen on shortening names, Mag, Madge and Rita too, changing vowels, Meg, producing rhymes, Peg, and then making pet forms, Maggie and Peggy.