I know the etymology, and although it’s listed as a noun, merriam-webster tells me the definition, but I want to know the name of this sort of adjective.

Wiktionary has it grouped as English Exocentric compound phrases, but that’s quite what I’m looking for.

Another example is the title of this book: Don’t Make Me Use My High School Teacher Voice, or the term ‘Big-Boy pants’, like “Time to put on your ‘big boy’ pants.”

Rather than use a straightforward adjective like “Seductive look” or “Annoyed” they use circumlocutionary language evoke a more complicated and particular situation, circumstance or role.

But is there a specific term for this type of adjective?