No, “prix” is the noun there, and it’s the same in the singular and the plural. The whole phrase, “grand prix” or “grands prix”, is following Modern French grammatical rules, where (1) the adjective sometimes does come before the noun, and (2) the adjective matches the noun in number and gender. So it’s odd, but in that case it’s only the adjective with “s” at the end.
In spite of those first words, I think we are generally agreeing 
In the army, generals live in private quarters, and privates live in general quarters.
And, as they get older, generals usually have problems with their privates.
I believe all of the general officer ranks were originally postpositive adjectives:
captain general
lieutenant general
sergeant major general
Over time, the “captain” got dropped, as did the “sergeant” from major general (but this is why a lieutenant general outranks a major general, even though a major outranks a lieutenant). Brigadier general/brigadier varies in different times and places from being the lowest ranking general officer to being a fancy colonel, sort of the land forces equivalent of “commodore”. Some armies also have a rank of “colonel general”, which is generally a high-ranking general officer rank–in the German rank system, just below a field marshal.
Well said…I learned some things therein. Now can I play too? How about “date certain” and “Sunday next” …
think of it as Several Attorneys in General, general i snot a rank, so it is not a noun it is general as in the definition here. Notice that rank [military] is the last and least definition =)
“RBI” is plural: Runs Batted In, RBI. There’s no need to say “RBIs.”
Ah, but RBIs is the plural of “Run Batted In.” 
Actually, “RBI” is treated as a word, and hence pluralized in the normal way.
See at the bottom of this page from the Baseball Almanac for the standard use of “RBIs.”
I know people use it that way, doesn’t make it right or a good idea. It’s usually more conversational contexts that do that, and indeed I’ve seen people read aloud from printed sources using an unmodified abbreviation, and they add the pluralization to say it.
Plenty of statistical discussion uses “RBI” in all instances. Similarly, “PA,” “HR,” etc.
See several places on this page from the Baseball Digest for the standard use of “RBI.”
And here’s a bit of trivia: the Surgeon General of the United States is actually a Vice Admiral.
Those Attorneys General work for the state, don’t they? So we don’t call them abogados, but fiscales. In the case of Spain, they’re not [attorney][adjective] but [attorney][of XYZ court], but if they were qualified with an adjective then yes, the adjective would show the plural (and gender, if relevant).
In translations, your Attorneys General are usually called “fiscal general del estado” or, if the translator wasn’t awake, “abogado general del estado”. Federal ones are called “fiscal federal” and DAs are called “fiscal del distrito” or plain “fiscal”. “The DA’s office” is “la oficina del fiscal”.
I’ve always wondered about Matthew Hopkins, the Witchfinder General. Is that use of General a noun or an adjective? What would the plural be?
From what I see in his Wikipedia page, it’s not that he was “a military boss who hunted witches” but “a witchhunter who performed his job all over the place”. Therefore, the “general” is the adjective and the plural would be Witchfinders General.
It is of course an inconsistency that in referring to “Attorneys General,” English follows the French form for the position of the adjective, but does not follow the French form of pluralizing the adjective as well as the noun.
However, “attorney general” did not come into English from Modern French, but from Anglo-Norman French, the language spoken and written in England for 200 or so years after 1066. I’m not sure that Anglo-Norman French added the “s” to adjectives with plural nouns, partly because it was influenced by several Germanic languages, including Middle English. Indeed, the words “Norman” and “Normandy” themselves are derived from Germanic origins – they were “North Men”, who had invaded northern France from Scandinavia, before William, Duke of Normandy, invaded England in 1066.
And what sportscaster has never said “Ribbies”? 
Not really. Postpositional adjectives are a legacy from “legal English”, i.e., the specialized vocabulary of the early Common Law courts, and they in turn drew heavily on Norman French, whose rules for adjective agreement were nowhere near as firmly ensconced as modern French’s. In any case, when a word, phrase, or usage is brought fully into English, it begins to obey English rules (including indeclinable adjectives) rather than those of its birth language (retention of the original plural being an occasional exception).
Just wanted to say I’m always glad to see a thread like this in Questions General.
The point is that the usage is not incorrect. It’s OK to treat an abbreviation as a word and pluralize it normally.