Definition of "Em"

And oh, Aunt Em! I'm so glad to be at home again!

1900 May 17, L[yman] Frank Baum, chapter 24, in The Wonderful Wizard of Oz, Chicago, Ill., New York, N.Y.: Geo[rge] M. Hill Co.

Mind you, he never calls me anything back. Isn't that the way of it? What do men call their wives. 'Em...' Like every woman in the planet was christened Emily. 'Em...is that shirt clean?'

2008, Anne Enright, Yesterday's Weather, Vintage, published 2009, page 4