Eatery is defined on OALD as:
a restaurant or other place that serves food
In that case, can I call McDonalds an eatery? Or can I call any single one restaurant in the city I see an eatery?
Eatery is a much less formal term than restaurant. It isn't a put-down, precisely, but you wouldn't call Spago or The Four Seasons an "eatery" except as a joke. On the other hand, you can certainly call McDonald's an "eatery", but that isn't the sort of establishment that is usually called that, either.
For me, "eatery" brings to mind a small place with a limited menu, possibly poor lighting, dinky countertops, and a, um, "chef" with a greasy apron and some sort of thick accent. But I might also use it as a catch-all term for a place that serves food, if I want to be deliberately vague about whether said place is a fancy sit-down restaurant, a less-fancy "family" restaurant, a diner, a thinly-disguised bar, a fast-food joint, or a roach coach.
For example, if we're driving up to the relatives -- an 8 hour drive if we're lucky and don't hit traffic on the outskirts of New York City --, around 5:00 p.m. I might be heard to say, "If we don't find an eatery soon, I'm gonna keel over from hunger."
I can't verify wheter "eatery" is more AmE or not. In any case it looks more AmE.Probably there is no waiter, there is no table cloth on the table, the furniture is cheap and so on. Word formation: With the ending -ery you can make up place names from verbs or nouns. In Italian the ending is -eria: pizza, pizzería, café, cafetería. In German the same ending is -erei: backen, Bäcker, Bäckerei. In English: to bake, baker, bakery. You can add the ending even to compound verbs. I found: to play out, playoutry - a place where games are played.
I have looked at various dictionaries, only The Free Dictionary says: 1900-1905, American. But in the meantime eatery is common in British English, too. There are two accepted spellings: eatery and eaterie.
Yes, you can call McDonald's and any restaraunt an eatery.
(eat + -ery "a place for eating")
(restaurant "food for restoring one's strength)