The word "archconservative" refers to someone who is extremely conservative, traditional, and opposed to progressive ideas. Therefore, the antonyms for this word would be liberal, progressive, radical or left-wing. A liberal person is open-minded, tolerant, and supports social and political reform. A progressive person also favors social and political reform, and is willing to adapt to new and evolving ideas. On the other hand, a radical person holds extreme views, often associated with revolutionary or extreme political or social change. And, a left-wing person is more liberal and progressive, concerned with social change, social justice, and equality. All these antonyms are diametrically opposite to the meaning of "archconservative" and represent a different set of beliefs and values.