a very upsetting or frightening dream

a terrifying nightmare 可怕的噩梦

I shouldn't have watched that movie - it'll give me nightmares. 我真不该看那部电影——它会让我做噩梦的。

an extremely unpleasant event or experience or possible event or experience

The whole journey was a nightmare - we lost our luggage and both flights were delayed. 整个旅程就像一场噩梦——我们弄丢了行李，而且两个航班都晚点了。

Being trapped underwater is my worst nightmare. 被困水下是我最害怕的事情。