In Greek mythology, the Nereids or Nereides (/ˈnɪəriɪdz/ NEER-ee-idz; Ancient Greek: Νηρηΐδες, romanized: Nērēḯdes; sg. Νηρηΐς, Nērēḯs, also Νημερτές) are sea nymphs (female spirits of sea waters), the 50 daughters of the 'Old Man of the Sea' Nereus and the Oceanid Doris, sisters to their brother Nerites.^[1] They often accompany Poseidon, the god of the sea, and can be friendly and helpful to sailors (such as the Argonauts in their search for the Golden Fleece).^[2]

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The synonyms Νηρηΐδες and Νημερτές are etymologically unrelated. Νηρηΐδες is a patronymic, describing them as the daughters of Nereus.^[3][4] Νημερτές means literally 'not-mistaking', and there is an adjective of the same form meaning 'clear', 'unmistakable', or 'true'.

The Nereids symbolized everything that is beautiful and kind about the sea. Their melodious voices sang as they danced around their father. They are represented as beautiful women, crowned with branches of red coral and dressed in white silk robes trimmed with gold.

These nymphs are particularly associated with the Aegean Sea, where they dwelt with their father Nereus in the depths within a golden palace.^[5] The most notable of them are Thetis, wife of Peleus and mother of Achilles; Amphitrite, wife of Poseidon and mother of Triton; Galatea, the vain love interest of the Cyclops Polyphemus, and lastly, Psamathe who became the mother of Phocus by King Aeacus of Aegina, and Theoclymenus and Theonoe by Proteus, a sea-god or king of Egypt.

In Homer's Iliad XVIII, when Thetis cries out in sympathy for the grief of Achilles for the slain Patroclus, her sisters appear.^[6] Four of her siblings, Cymodoce, Thalia, Nesaea and Spio were also among the nymphs in the train of Cyrene.^[7] Later on, these four together with their other sisters Thetis, Melite and Panopea, were able to help the hero Aeneas and his crew during a storm.^[8]

In one account, Cassiopeia boasted that her daughter Andromeda was more beautiful than the Nereides, who were enraged by the claim. Poseidon, in sympathy for them, sent a flood and a sea monster to the land of the Aethiopians, demanding as well the sacrifice of the princess.^[9] These sea goddesses also were said to reveal to men the mysteries of Dionysus and Persephone.^[10][11]

This list is correlated from four sources: Homer's Iliad,^[12] Hesiod's Theogony,^[13] the Bibliotheca of Pseudo-Apollodorus^[14] and the Fabulae of Hyginus.^[15] Because of this, the total number of names goes beyond fifty.^[16]

In ancient art the Nereides appear in the retinue of Poseidon, Amphitrite, Thetis and other sea-divinities. On black-figure Greek vases they appear fully clothed, such as on a Corinthian hydra (sixth century BCE; Paris) where they stand near the bier of Achilles. Later vase-paintings depict them nude or partially nude, mounted on dolphins, sea-horses or other marine creatures, and often grouped together with Tritons. They appear as such on Roman frescoes and sarcophagi. An Etruscan bronze cista from Palestrina depicts winged Nereides.

Famous is the Nereid Monument, a marble tomb from Xanthos (Lycia, Asia Minor), partially in the collection of the British Museum. At the top is a small temple surrounded by pillars between which Nereides stood. They were depicted in motion and with billowing, transparent clothes. The style is Attic-Ionian and dates to c. 400 BCE.

In the Renaissance and baroque periods the Nereid was frequently used to decorate fountains and garden monuments.

Nereides were worshiped in several parts of Greece, but more especially in seaport towns, such as Cardamyle,^[41] and on the Isthmus of Corinth.^[42] The epithets given them by the poets refer partly to their beauty and partly to their place of abode.

In modern Greek folklore, the term "nereid" (νεράιδα, neráida) has come to be used for all nymphs, fairies, or mermaids, not merely nymphs of the sea.^[43]

Nereid, a moon of the planet Neptune, is named after the Nereids, as is Nereid Lake in Antarctica.^[44]

• Neraida (type of supernatural wife)