It's a Japanese only, AKA NA Adjective.

That would explain why it is not in my list.

Why the misleading thread title, then?

I didn't think about it. I suppose I should have said "英語品詞日本語で" but I was just thinking of the literal translation of "Parts of Speech in Japanese." There was no intent to mislead. I said exactly what the list was in my first post.

U should have written 英語の品詞、日本語での正式名称

Regardless, my intent is now clear. I still believe what I provided was somewhat helpful. My own Japanese studies are outside the Internet. Just trying to be helpful to others.

Tsuwabuki, I think English speakers tend to learn 形容動詞 as な形容詞. I think I was taught い形容詞 and な形容詞 as the terminology back maybe my first or second year, primarily because we called them (in English), na-adjectives and i-adjectives.