Rumen is a queasy, first-stirrings-of-nausea sort of a word.
This isn't surprising, because the rumen is the first stomach of an animal like a cow or a buffalo (which are both ruminants, geddit?). The rumen starts the process of digesting the animal's food, and then the food is sicked back up into the animal's mouth (lovely!) so it can be chewed again.
Oh, how different our table manners would be if we all ate grass...
Ruminating, if you're a ruminant, is the re-chewing of this partly-digested food, which has the nice name of cud.
If you're a human, however, ruminating usually means thinking about something; and what I'm thinking is that being a ruminant may sound pretty disgusting, but it's not at disgusting as the system faviured by rabbits, who also put their food through their innards twice, but do it by eating their own poo.
Word Not To Use Today: rumen. Well, let's face it, why would anyone want to use the word rumen? Rumen is a Latin word and it means throat or gullet.