Obvious, but it never occurred to me until an chance conversation with my oldest daughter that 'Cafe' is French for Coffee. M-W says before that it came from the Turkish 'kahve'. I had heard of 'cafes' growing up and always inferred that they were smallish, which agrees with m-w.
It also Spanish for coffee, and also "coffee colored" or tan/beige.
Cafeteria, OTOH, well, I'll copy m-w here:
"Etymology: American Spanish cafetería coffeehouse, from cafetera coffee maker, from French cafetière, from café"
So I grew up calling the school lunch room a cafeteria.
I grew up with that, too, and they still use it in schools around here. It's pretty much the general term for a room where you can buy your food and sit down, as opposed to a "food court" (at a mall) where there is a choice of vendors, or outside at a festival of some kind. Cafeterias are self-contained, in our usage.
But also there were places like "The Blue Boar" that my grandparents loved to go to that were called cafeterias where they had buffet-style. However, those buffets were different than the modern ones in that you paid for each trip - and the food was already portioned out on plates for you. You would take a tray up and get several different plates and then you would pay for each individual item on the plate.
As a child on a trip to Europe, we stayed at an inn called The Blue Boar, so it brings back those memories to see the name, even though "mine" was in Malden, Essex. We stayed there before crossing the channel to visit Belgium, Germany, Denmark and Holland.
Buffet I guess means table or board or something like that. It doesn't mean "all you can eat" (at least that's not the etymology). It means "things on a table, ready to eat."
It seems no one knows the origin of "buffet". Here's a made-up idea: "buffet" (BUH - fet) means to jostle, and if you are at a buffet, you might get jostled... Okay, a probably a bit too modern, but perhaps the idea of a table or piece of furniture with many serving dishes on it jostling each other trying to fit. It's plausible, anyway!
When we moved to AK, there was I recall, on Post, (Ft. Wainwright) a "groceteria" which was often shortened to "the grosh" or "the gross." It was indistinguishable from what we would call today, "a convience store." I've never been to another place that referred to "groceteria." Grocery comes (m-w again) from Anglo-French 'groser' or wholesaler. I recall the first day in our new housing, being sent to the 'gross' with $5 to buy 1 loaf bread and 1 half gallon milk - and coming back with just a little change. My parents had trouble believing I didn't buy something else with it. (This was 35 years ago. It does not seem so incredible now.)
Now that's just gross! It really does sound funny to my ears. It's not a word in (standard) Spanish, although a homophone is "grosería", which means something rude (gross/coarse). In Spanish the suffix "-ería" often denotes a venue that sells whatever the root part is, for example:
zapatería (zapato = shoe),
panadería (pan = bread) and so on. (Hence, also, "cafetería"...)
There was an army hospital not too far from there that had a kind of cafeteria in its basement. It was a lunchroom with only vending machines. Hot and cold sandwiches, maybe soups, chips, drinks, etc. I can't remember if there was a special name for it. I think this might have been a throwback to an earlier era.
The first time I ever saw one of these was in Europe as a child. We must have been whining about being hungry and my parents desperately looking around (waaaaaay before "fast food" joints we know today), and I was fascinated by the glass revolving cases, the pre-made sandwiches and the novelty of it all! I think it was in Holland (help, Bran!), and called an "automat".
Regarding "diner," I note that m-w does not include a definition that means "a restaurant." I'm not sure the difference between a diner and a cafe, except I always saw a diner as more home-brew American and cafe as more cosmopolitan. I don't know whether I have correctly inferred the distinction.
To me diners are along the lines of truck stop restaurants; homemade, basic (fattening) "comfort" food; inexpensive, but usually pretty good, with the requisite good coffee. As you say, a cafe to me is upscale, less food, more different kinds of coffee and desserts.
Restaurant come from French 'restore.' That kinda makes sense.
Didn't know this; it makes a lot of sense! Especially for "break-fast"!