This is the 19156th most frequent Korean word.
악몽이었을
"It was a nightmare."
The term '악몽이었을' here is used to discuss a hypothetical past event related to a nightmare, stressing the uncertain yet reasonable conclusion.
어젯밤 꿈은 정말 무서운 악몽이었을 거예요.
Last night's dream must have been a really scary nightmare.
'악몽이었을' denotes the possibility of an event being classified as a nightmare in this context.
그 일이 악몽이었을 수 있다는 생각은 나를 오히려 안심하게 했다.
The thought that it might have been a nightmare instead actually reassured me.
Here, '악몽이었을' emphasizes a hypothetical wish regarding past occurrences being simply a nightmare.