Oceanus and Tethys (or Atlas and Pleione) who were transformed into a cluster of stars (now several hundred stars in the constellation Taurus). There have been two main theories behind their name. The first derives it from hyein, 'to rain', since it was believed that when the constellation 'rose' simultaneously with the sun, rain and stormy weather would follow.
The Romans, however, derived the name from hys, 'pig', and consequently translated it as Suculae (literally, 'piglets'). This unlikely interpretation sprang not merely from the resemblance of the word to the name but because the constellation was seen pictorially as a sow with her piglets.
Pliny even combined both possibilities, saying that the rain presaged by the Hyades made the roads so muddy and miry that the stars seemed to delight in the dirt, like pigs! Another explanation says that the sisters wept copiously for their brother Hyas, who had been killed by a boar, and so were together known by his name. (In fact, as in many cases, his name was almost certainly invented to explain their name.) Yet another explanation rather ingeniously derives their name from its first letter, the Greek upsilon, since the stars form a figure that resembles this letter.