John Tzetzes, Allegories of the Odyssey 4.52-69
The names of Proteus and Eidothea are made up, as your main man Tzetzes has long thought. Look at what he has to say to you: Proteus is the water, the foremost of all the elements; thus he receives the titles of old man and of the mighty. If he took human form, he would say that he was an old man, but wise or something else like that, but certainly not of the mighty. Thus old uncle Tzetzes thinks that Proteus is water, while Eidothea is a name fitting the most prophetic, such as astrologers and all of the other people in the prognosticating line. For Eidothea knows everything like a god or a knowing goddess; professor Tzetzes is telling you that she is the diviner. The daughter of Proteus is so called because she knows everything in advance from hydromancy. In the Homeric telling, she is said to have foretold everything to Menelaus, explaining how Proteus was her father, so that he could do a bit of prophecy for him. He says that this is just what happened. Tzetzes notes that she’s the one who saw Menelaus.