名詞 nightmare:

1. a situation resembling a terrifying dream
   同義詞：incubus
2. a terrifying or deeply upsetting dream

1. The nightmare gave her the creeps.
   那場惡夢使她不寒而栗。
2. I had a nightmare and cried out in horror.
   我做了一個惡夢，驚恐地大叫。
3. Driving during the blizzard was a nightmare.
   在暴風雪中開車真嚇人。
4. I have nightmares about falling off a cliff.
   我常做惡夢夢見從懸崖上摔下來。

night.mare

n.（名詞）
A dream arousing feelings of intense fear, horror, and distress.
惡夢：使人恐懼、害怕和痛苦的夢
An event or experience that is intensely distressing.
使人極其痛苦的事情或經歷
A demon or spirit once thought to plague sleeping people.
夢魔：被認為折磨睡覺的人的魔鬼或靈魂

來源：
Middle English [a female demon that afflicts sleeping people]
中古英語 [折磨睡著的人的女妖精]
night [night] * see night
night [夜晚] *參見 night
mare [goblin] from Old English * see mer-
mare [妖怪] 源自 古英語 *參見 mer-

【引伸】
night.mar.ish
adj.（形容詞）
night.mar.ishly
adv.（副詞）
night.mar.ishness
n.（名詞）