Double barrel names can be made up of any two names. Very often the separate meanings of the two root names do not make sense when combined together, so we shall look at them separately. Billie was originally found as Billy and was the pet form of the popular masculine name William which is of German origin and means ‘Protector’. The pet form became a name in its own right and later became a name for girls, with the feminine spelling Billie emerging. Jo is a short form of names such as Josephine or Joanna, both ultimately from the same root as the masculine name Joseph which is Hebrew and means ‘God will Expand the Land’.