If you say that something is dreadful, you mean that it is very bad or unpleasant, or very poor in quality.
awful , appalling
They told us the dreadful news.
他们告诉了我们这个坏消息。
Dreadful is used to emphasize the degree or extent of something bad.
terrible
We've made a dreadful mistake.
我们犯了一个很大的错误。