Egeria (Latin: Ēgeria) was a nymph attributed a legendary role in the early history of Rome as a divine consort and counselor of Numa Pompilius, the second Sabine king of Rome, to whom she imparted laws and rituals pertaining to ancient Roman religion. Her name is used as an eponym for a female advisor or counselor.
Egeria may predate Roman myth: she could have been of Italic origin in the sacred forest of Aricia in Latium, her immemorial site, which was equally the grove of Diana Nemorensis ("Diana of Nemi"). At Aricia there was also a Manius Egerius, a male counterpart of Egeria.
The name Egeria has been diversely interpreted; it might mean "of the black poplar"; Georges Dumézil proposed it came from "e-gerere", suggesting it came from her childbirth role, though this sounds very unlikely; her role as prophetess and author of "sacred books" would compare her to the Etruscan figure of Vegoia (alleged author among other things of "Libri Fulgurales", which give keys to interpreting the meaning of lightning strokes, seen as ominous messages from deities, a variety of them).
Egeria as a nymph or minor goddess of the Roman religious system is of unclear origin; she is consistently, though not in a very clear way, associated with another figure of the Diana type; their cult is known to have been celebrated at sacred groves, such as the site of Nemi at Aricia, and another one close to Rome (see section below); both goddesses are also associated with water bearing wondrous, religious or medical properties (the source in that grove at Rome was dedicated to the exclusive use of the Vestals); their cult was associated with other, male figures of even more obscure meaning, such as one named Virbius, or a Manius Egerius, presumably a youthful male, that anyway in later years was identified with figures like Atys or Hippolyte, because of the Diana reference (see Frazer).