Tethys was the daughter of Uranus and Gaia and the wife of Oceanus, to whom she bore a vast number of offspring, including most of the river-gods and their three thousand (!) sisters, the Oceanids.

Her name is popularly derived from tethe, 'grandmother' (perhaps more 'grand mother'), a word apparently related to tittho, 'nurse', 'teat', or tithene, 'nurse'. On the other hand her name could also be linked with tithemi, 'to place', 'put', 'order' (compare Themis and Thetis), so that she is a 'determiner' or 'disposer'.