Hi /u/OccamsComb!
The word “attorney general” consist of a noun – attorney – and an adjective modifying said noun – general.
In some languages, modifying a noun requires the speaker to modify the attached adjective as well.
For example, a ~~blue~~ red book would be *un livre rouge* in French. If we take the plural in English, we get ~~blue~~ red books, while in French we get *les livres rouge***s**.
As you may notice, both the noun *and* the adjective get transformed into plural forms in French, while the adjective remains unchanged in English.
Applying the same logic to attorney general, we modify the noun to its plural form – attoneys – and leave the adjective unchanged –general. Putting the words back together thus yields *attorneys general*.
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