Merriam-Webster's Word of the Day for March 24, 2017 is:
nightmare \NYTE-mair\ noun
1 : an evil spirit formerly thought to oppress people during sleep
2 : a frightening dream that usually awakens the sleeper
3 : something (such as an experience, situation, or object) having the monstrous character of a nightmare or producing a feeling of anxiety or terror
Since starting the new medication, John routinely experiences vivid dreams when he sleeps and even suffers from frequent nightmares.
"The dream of a stress-free, short-term rental in a balmy locale can easily become a nightmare without due diligence, according to real estate agents and Long Island snowbirds." — Cara S. Trager, Newsday, 19 Feb. 2017
Did you know?
Looking at nightmare, you might guess that it is a compound formed from night and mare. If so, your guess is correct. But while the night in nightmare makes sense, the mare part is less obvious. Most English speakers know mare as a word for a female horse or similar equine animal, but the mare of nightmare is a different word, an obsolete one referring to an evil spirit that was once thought to produce feelings of suffocation in people while they slept. By the 14th century the mare was also known as nightmare, and by the late 16th century nightmare was also being applied to the feelings of distress caused by the spirit, and then to frightening or unpleasant dreams.