Of uncertain origin. From the 18th century it is clearly used as a pet form of Ann (see Nan), but it may originally have been a similar formation deriving from the common medieval given name Annis, a vernacular form of Agnes. Nowadays it is an independent name, and was especially popular in America in the 1930s, 40s, and 50s. A meaning of the name Nancy is Grace.
English and Welsh: patronymic from the Middle English personal name Jon(e) (see John). The surname is especially common in Wales and southern central England. In North America this name has absorbed various cognate and like-sounding surnames from other languages. (For forms, see Hanks and Hodges 1988).