Tethis (Greek: Τηθύς, transl.: Tēthýs), in Greek mythology, was a titanid, daughter of Uranus and Gaia. From her union with her brother Ocean, the oceânides were born.
The oceânides number three thousand, and they also had three thousand rivers as their children. She personifies the fruitfulness of water, which nourishes bodies and forms the sap of vegetation.
Thetis cared for Hera, handed over to her by Reia during the struggle between titans and the Olympian gods. In recognition, the queen of Olympus reconciled her with Oceanus, when the couple fell out. Thetis is depicted as a young, wise-looking woman. She rides around the world in an ivory shell, pulled by white horses.
The name of the Titanid Thetis is the same in Portuguese as her granddaughter, the Nereid Thetis, daughter of Doris (one of the Oceanids) and mother of Achilles. However in Greek the names are different: the titanid is written Τηθύς (tethys) and the nereid Θέτις (thetis).