DAH-noo
The shadowy mother-goddess from whom the Tuatha Dé Danann — "the people of the goddess Danu" — take their name.
Danu is barely narrated in the surviving texts at all; she appears nowhere as a character with her own adventures, only as the ancestral figure the entire Tuatha Dé Danann are named for. Some medieval genealogists identify her with Anu, a goddess associated with prosperity and the land, and later folklore ties her name to rivers and abundance across the Indo-European world.
That thinness is itself the point: Danu functions less as an active goddess in the stories and more as the root the whole pantheon's identity grows from — a reminder that "Tuatha Dé Danann" is a lineage claim as much as a list of names.