The usual way to modify a noun in English is to put an adjective before the noun: nice view, tasty treat, hot day. But every once in a while, we put the adjective after the noun. Often this is because it comes from a language where adjective-after-noun is the norm, namely French. Much of our legal and military terminology comes from French and Latin, and some noun-adjective compounds, like "attorney general," came with it. This leads to a situation where the act of putting the modifier after the noun becomes a mark of authority and importance, even with regular English words.
Time immemorial, words unspoken, lands unknown (and phrases similar) take on a loftier quality than their mundane reversed counterparts. It also leads to some plurals that work in unexpected ways. Here are 26 of them.
1. ATTORNEYS GENERAL
Also postmasters, secretaries, consuls, and surgeons general. The "general" in these compounds originated as an adjective opposed to "special" or "particular." In the U.K. it is commonly pluralized as "attorney generals," but in the U.S. we have decided to dig in our etymological heels and make an example of this plural within a compound.
Here "martial" is the adjective for military. So "courts-martial" is preferred, but "court-martials" is also acceptable.
3. NOTARIES PUBLIC
"Notary publics" is also used, but "notaries public" sounds that much more official.
4. SENATORS ELECT
"Elect" is one of those Latin-flavored adjectives that make everything seem a touch more important.
5. SERGEANTS MAJOR
"Sergeant majors" is also acceptable.
6. SUMS TOTAL
This was more common in the 19th century, before "total" became a noun.
7. FEES SIMPLE
In legal terms a fee (related to "fief") is an owned piece of land, and "simple" is an adjective meaning without complications, free and clear from other claims on it.
8. HEIRS APPARENT
Heirs apparent (first in line regardless of whether anyone else will be born) have a leg up on heirs presumptive (first in line unless any heirs apparent are born).
9. BODIES POLITIC
Over the centuries "body politic" has been used to refer to offices held by individuals that are passed down through succession (King, Bishop, Abbot), society considered as a whole, or the state/nation. In each case, "politic" is an adjective.
The "errant" in "knight-errant" — that staple of medieval literature, the wandering, adventure-seeking knight — goes back to the same root as "itinerant" and "itinerary," Latin iter, journey.
11. POETS LAUREATE
"Laureate" is an adjective from the Latin for "crowned with a laurel." Careful with this one, though. Don't go crazy and start saying "Nobels laureate." A "poet laureate" is a poet, but a Nobel laureate is not a Nobel. Use "Nobel laureates." And if you want to seem less hifalutin,' use "poet laureates" too.
12. PROFESSORS EMERITI
One "professor emeritus," two "professors emeritus." But if you want to go whole hog, use "professors emeriti" with the Latin plural adjective. Your professors emeriti will love it.
13. PERSONAE NON GRATAE
There are a few acceptable ways to pluralize "persona non grata," the Latin term for unwelcome person. It's often used as a whole descriptive phrase for a plural ("they were persona non grata") or pluralized in English (personas non grata). The proper, full-on Latin plural ("persona" being a feminine noun) is "personae non gratae."
14. CURRICULA VITAE
"Curriculum vitae" means "course of life" in Latin. Some go with "curriculums vitae" on this, while others take up the Latin plural "curricula vitae." And a few push it a little too far with "curriculum vitarum" (courses of lives). When in doubt, use "CVs."
"Cul-de-sac" comes from the French for "bottom of a bag" – that's "bottom" as in "booty." Cul-de-sacs is a perfectly acceptable plural in English, but culs-de-sac has a little more je ne sais quoi.
16. AGENTS PROVOCATEURS
In this French phrase for infiltrators trying to stir things up, both the noun and the adjective take an 's'.
17. FEMMES FATALES
Likewise for this one.
18. COUPS D'ÉTAT
A coup is a blow or strike. In English we follow the French way of not pronouncing the "p" in "coup d'état," and in the plural, we add another unpronounced French letter just for good measure. (Same for "coups de grace.")
19. FORCES MAJEURES
A legal term for "act of God" or unforeseen major disaster. Again, both the noun and the adjective get pluralized.
20. FILMS NOIRS
"Film noirs" is perfectly good English. "Films noir" is a commonly used hybrid. "Films noirs" is how to do it à la française.
21. BATTLES ROYAL
Be advised: Don't try this in the world of professional wrestling, where it's "battle royals."
There are a whole set of English words that are not exactly of the form "noun adjective" but they have a noun followed by a modifier of some kind, usually a prepositional phrase. In these cases, the plural can go on the end, or on the noun.
English has no problem turning even bigger phrases into nouns and pluralizing them the normal way ("ne'er-do-wells" "forget-me-nots"), but when there's a noun inside a set phrase, we get unsure of ourselves. "Johnny-come-latelies" works, but so does the "Johnnies" version. (See also, "sticks-in-the-mud," "Jacks-in-the-box").