Except: trừ, ngoại trừ

Trừ means "except": it takes someone or something out of what you've just said. Put it after the main statement: Ai cũng đi, trừ anh Nam. Everyone's going except Nam. Quán mở cửa mỗi ngày, trừ thứ hai. The shop's open every day except Monday. The main statement usually has an "all" in it, such as ai cũng (everyone) or mỗi ngày (every day), and trừ takes something away from it.

It can also start the sentence, often with ra after the exception: Trừ sầu riêng ra, trái cây gì em cũng thích. Apart from durian, I like every fruit.

Ngoại trừ means the same and sounds more formal, so you'll see it in notices and at work: Tất cả phải có mặt, ngoại trừ người nghỉ phép.

Its opposite is kể cả (including): Ai cũng đi, kể cả anh Nam. For "unless", followed by a whole sentence, use trừ khi: Em sẽ tới, trừ khi phải tăng ca. On its own, trừ is also the verb "subtract" or "deduct": Mười trừ ba là bảy. Ten minus three is seven.