State Attorneys General
The words "state" and "general" are adjectives, which do not have plural forms ("my red shoes" as opposed to "my reds shoes"), thus the noun, "Attorney" is the only word to change to the plural.
- "State" here is an appositive noun, which means it is a noun that acts like an adjective (as in "dog food", whereby the appositive noun "dog" describes "food"), thus, as an adjective, it does not pluralize with "attorneys".
- "General" here is the adjective meaning "chief", "main," or "principle" (as in "the general idea") and not the noun for a military commander, thus, as an adjective, it does not pluralize with "attorneys".
The reason for the adjective "general" following the noun and not preceding it, as is the usual practice in English, is that the Normans brought the French noun-adjective form with them, but the Old English adjective-noun form stuck, leaving a few remnant French-derived adjectives that follow the noun. (Interestingly, in French, adjectives that precede the noun have a different meaning from the same word that follows a noun, such as "un grand homme" for "great man" versus "un homme grand" meaning "tall man".)
So it's easy to remember: the last word in "attorney general," "surgeon general" "love supreme", "time remembered," "death foretold," "agent provocateur," etc. is an adjective, thus pluralize only the noun and not the adjective ("agents provocateur").
I'm sure there's a technical word for these types of adjectives, but it's buried somewhere I can't find in my rather large Cambridge grammar book.