The root word is “pizza,” obviously. Seems simpler just to add “ria” at the end.
Plural?
i.e., pizzeria is a word in Italian, and the Italian plural is pizze.
So presumably the fully-formed word pizzeria was adopted from Italian.
Because the people who decide these things about words have no common sense! Probably the same people who prefer the English system of measurement as opposed to the metric system.
Well, why are pizzicati not pizzecati?
Same etymology (pinch or pluck).
I would guess this is it. The plural of pizza in Italian is pizze, so a pizzeria is a place where multiple pizzas are sold.
In that case, why is the singular not pizzecato?
Quick Italian grammar lesson: singular nouns ending in -a have the plural -e; nouns ending in -o or -e have the plural -i. There are exceptions (for example, the plural of “uomo” (man) is “uomini”), but you get the idea.
But what I want to know is, why is it “spaghetti,” “linguini,” and “rigatoni,” which are plural, but “lasagna,” which is singular? There’s more than one lasagna noodle used in a serving; shouldn’t it be “lasagne”?
I have seen “lasagne” noodles on some grocery shelves and wondered what the diff was. Thanx, That-a Don-o Guy-o. 
Is “salami” singular or plural? Which language and which “rules” are followed? Same issue.
Because the name of the dish is lasagna. The noodles are named after the dish, not the other way round.
In Italian it’s the plural of salame. English borrowed the plural and made it singular.
No no no no no, that word is not a compound of the noun “pizza/pizze” with “cato/cati”. It’s the past participle of the verb “pizzicare”, “to pinch or pluck”. You can’t stick a noun plural into the middle of a verb form.
The singular is “pizzicato”, because it’s the same past participle of the verb “pizzicare”, just in the singular form.
Apologies if all of this was just a joke and I got whooshed.
You are not alone, I was still unsure if this was serious, but was leaning toward joke.
I take it back. I didn’t research far enough.
Nope. The Italian word is a combination of the generic noun “pizza” with the suffix “-eria”, cognate with the English “-ery” as in “bakery”, “eatery”, “creamery”, “nunnery”, both ultimately from Latin “-oria”.
The final “a” of “pizza” assimilates to the initial “e” of “-eria”. Nothing to do with how many pizzas are sold in the pizzeria.
Thanks - I can’t believe the similarity to -ery didn’t occur to me, it’s so obvious now that you’ve pointed it out.
Because you’re supposed to pronounce it like Sal the Stockbroker.
Sure, but what if I’m opening a very special shop that will only ever sell one pizza? Can I call it a pizzaria then?
No, in Italian the name of the dish is lasagne (or, in full, lasagne al forno, “oven-baked lasagnas”).
I usually see it spelt “lasagne” in Britain, but the usual American form seems to be “lasagna”.
You have my permission. How much for the pizza?