Noun or adjective?

For future reference, note that only a noun, pronoun, or any noun equivalent can function as the subject of a sentence.

Aspara GusFor future reference, note that ...

Odd, though, isn't it? "green" is an "adjective promoted to a noun (equivalent)" in this case, I suppose.

CalifJimOdd, though, isn't it? "green" is an "adjective promoted to a noun (equivalent)" in this case, I suppose.

According to the Shorter Oxford Dictionary, that happened in Middle English, so we're cool.

enoonAccording to the Shorter Oxford Dictionary, that happened in Middle English, so we're cool.

I'm so relieved, but a bit trepidatious about asking what the Longer Oxford Dictionary says.

CalifJimI'm so relieved, but a bit trepidatious about asking what the Longer Oxford Dictionary says.

Me, too. Thank *** I could only afford the shorter one.