20Monaghan, Patricia. The Encyclopedia of Celtic Mythology and Folklore. New York: Facts On File, 2003. 20.
In its entry on Danu, the Encyclopedia explains, "Danu's name has been derived from the Old Celtic dan, meaning "knowledge," and she has been linked to the Welsh mother goddess DÔN. Some texts call her the daughter of the mighty DAGDA, the good god of abundance, a connection that supports the contention that she was an ancient goddess of the land's fertility." (p. 117)
The Wikipedia entry for Anann adds, "As a goddess of cattle, she is responsible for culling the weak. She is therefore often referred to as 'Gentle Annie,' in an effort to avoid offense, a tactic which is similar to referring to the fairies as 'The Good People.'
Another sources suggests the original name for this Celtic mother-goddess "seems to have been Dánuv, which again is attested by a goddess-name among various Indo-European peoples (Indic Dánu, Greek Danaë)." (Ó hÓgáin, Dáithí. "Patronage and Devotion in Ancient Irish Religion." History Ireland 8.4 (2000): 20-24.)