NIGHTMARE - [noun] a terrible dream; a terrible event or experience
Examples of use
Her small daughter woke up in tears, because she had a nightmare.
The journey home was a nightmare! Traffic jams every freaking five minutes, and then the car broke down.
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English speaking practise
Remember that if you don't use that word in English conversations or writing you'll forget it in a short time. So the best thing you can do to learn this word is just trying to use it in speaking or writing. Remember also that practise is the key to fluent english speaking.
You can always find a partner, who would also like to improve his/her