what is the rhetorical figure of speech equivalent to eponym or alliteration or metaphor for when you have used a name for one class of objects (yes, technically a centaur is sentient but think of it in the way human or chair is a class of object) as the given name for a wholly different group of objects.Well, it's not
alliteration or
metaphor. Centaurus was not a centaur. He was human or divine. He mated with some mares and that's where centaurs came from, or at least that is the myth preserved for us in classical literature. Sounds like a plain old eponym. Centaurs are also called Ixcionides, i.e., the sons of Ixion. His story (
link) is complicated, but he was human or semi-divine, being the offspring of Zeus. As implied below,
genericization comes close, but is a modern term. Do you have any other wexample than centaurs, which I believe is a flawed one?
Many origin myths (of groups of people or other kinds of beings) merely postulate a forefather whose name is a back-formation from the group name, e.g., Geoffrey of Monmouth writes that the origin of the Britons is from a Trojan Brutus, who left Asia with Aeneas (the latter having founded Rome), and finally ended up in Britannia. Another example is Romulus who founded Rome with his twin brother Remus.
