fem. proper name, Old English Mildðryð, from milde "mild" (see mild) + ðryð "power, strength." A popular name in the Middle Ages through fame of St. Mildred (obit c. 700), abbess, daughter of a Mercian king and a Kentish princess. Among the 10 most popular names for girls born in the U.S. between 1903 and 1926, it hasn't been in the top 1,000 since 1983.