From an Old English female personal name Mildþrӯð, derived from mild ‘gentle’ + þrӯð ‘strength’. This was the name of a 7th-century abbess, who had a less famous but equally saintly elder sister called Mildburh and a younger sister called Mildgӯð; all were daughters of a certain Queen Ermenburh. Their names illustrate clearly the Old English pattern of combining and recombining the same small group of name elements within a single family. This name was in fairly regular localized use until the early 18th century and it enjoyed a strong revival throughout England in the 19th century. Its use declined from the 1930s onwards.
German, Dutch, and Jewish (Ashkenazic): occupational name for a maker of copper cooking vessels, from an agent derivative of Middle High German kezzel ‘kettle’, ‘cauldron’, Middle Dutch ketel, modern German Kessel.