de-ys

O.E. dæge "female servant, housekeeper, maid," from P.Gmc. *daigjon, from PIE *dheigh-. Now obsolete (though O.E.D. says, "Still in living use in parts of Scotland"), it forms the first element of dairy and the second of lady. The ground sense seems to be "kneader, maker of bread;" advancing by O.N. deigja and M.E. daie to mean "female servant, woman employed in a house or on a farm." Dæge as "servant" is the second element in many surnames ending in -day (e.g. Faraday, and perhaps Doubleday "servant of the Twin," etc.).