Select the correct one-word substitute for the given phrase:

A person who attacks or criticizes cherished beliefs, customs, or traditional institutions

The correct answer is Iconoclast.

Explanation:

Let us analyze the definitions of all the given options:

1. Iconoclast: A person who attacks or criticizes cherished beliefs, customs, or traditional institutions. This perfectly matches the given phrase.

2. Dogmatist: A person who asserts opinions as indisputable truth without consideration of evidence or the opinions of others.

3. Conformist: A person who conforms to accepted rules, behaviors, or established social practices.

4. Traditionalist: A person who adheres strictly to or advocates for traditional beliefs, customs, and practices.

Hence, the correct one-word substitute is Iconoclast.