Phorcys and Ceto. Their names were Enyo, Deino and Pemphredo (see the disagreeable meanings of these). If anything, they were even more sinister than the Gorgons since they were born as old women.
Their name, thus, seems to be from the root of grays, 'old woman'. As Hesiod described it in his Theogony, 'They came into the world with white hair; that is why they are called Graiae by both gods and men.' (The English word 'grey' is not related to their name, even though the old women had grey hair.)