Someone who is irreligious is against religion, or has no religious feeling. The word can describe a person, a book, a joke, or a whole time in history. It is a fairly careful, bookish word. It is stronger than just “does not go to church”: a person can skip services and still feel religious; an irreligious person does not have that feeling, or pushes against it. Though actually, English also has words like non-religious and secular, which often mean “not tied to a religion” without the extra bite of being opposed. Irreligious can cover both “has no faith” and “is hostile to faith,” so you have to hear the tone.

不信教的、沒有宗教情懷的；若帶反對意味，則是「反宗教的」