So. "An eponym is the name of a person ... after which a particular place, tribe, etc. is named or thought to be named. One who is referred to as eponymous is someone who gives his or her name to something, e.g., Julian, the eponymous owner of the famous restaurant Julian's Castle."

What do you call it when a general name for a group of things or a thing is used to name another thing. For example: a hybrid human/horse is named a centaur (yes, yes they're mythological) and a sort of small planet that's a hybrid asteroid/comet is named a centaur in their honor. So what is that second use of centaur called as a part of speech? Anyone? anyone?

Yes I really want to know: NOT a rhetorical question.

Thanks.