the same night; that night
Used in news reports and formal contexts to refer to a night previously mentioned. Often adverbial, meaning 'on the same night' or 'that night'.
同夜、都内で別の事件が発生した。
That same night, another incident occurred in the city.
That night, a fire broke out in a nearby warehouse.
The press conference was held that night.
At around 11 p.m. that night, a suspicious person was seen near the scene.
当夜 means 'the night in question' and looks similar to 同夜, but 当夜 emphasizes the night of a specific event rather than referring back to a previously mentioned night.
Compound of 同 (どう, 'same') and 夜 (や, 'night').