In Euripides' Medea, which was first staged in 431 BCE in Athens, the play opens with a lamentation by Medea's nurse, who wishes that Jason and the Argonauts had never come to Colchis, Medea's native land.
Oh how I wish that ship the Argo
had never sailed off to the land of Colchis,
past the Symplegades, those dark dancing rocks
which smash boats sailing through the Hellespont.
(Ian Johnston translation)
Medea's nurse is an elderly servant who would have nursed Medea when Medea was a baby. It seems to have been common in some ancient societies for a woman other than the child's mother to nurse the child. In addition to nursing the infant child, the nurse would have remained with the child's servant as long as the nurse and the child remained alive. Compare Homer's Odyssey, where Odysseus' nurse is still alive and well in his palace after many years.
In plays like Euripides' Hippolytus, the nurse serves as a confidant for her mistress Phaedra, eventually persuading her to confess her love for her stepson Hippolytus and make an indecent proposal to the young man.
In Medea, however, the title character serves to help provide background for the play and explain Medea's current mood. Medea's nurse does not have a speaking role in the last four-fifths of the play.