昨夜 means "last night." This word has two standard readings with different registers.
READINGS:
- さくや: formal, written, news
- ゆうべ: casual, spoken, everyday
COMMON PATTERNS:
- 昨夜の出来事: last night's events
- 昨夜から: since last night
- 昨夜遅く: late last night
SIMILAR TIME WORDS:
REGISTER:
さくや is preferred in news reports, formal writing, and literature. In conversation, ゆうべ is more natural.