Happening or done in the same period of time. Two wars can be contemporaneous; a letter can be contemporaneous with the events it talks about. This is a formal word, much loved by historians.

Happening or done in the same period of time在同一段時間裡發生或完成。Two wars can be contemporaneous兩場戰爭可以是 contemporaneous（同時期的）; a letter can be contemporaneous with the events it talks about一封信也可以跟它所談論的事件是同一個時期的。This is a formal word, much loved by historians這是個正式的詞，歷史學家特別愛用。

In everyday English people say at the same time.

In everyday English在日常英文裡 people say at the same time人們會說 at the same time。

Though actually it is not the same as contemporary. Contemporary is the common word, and it has a second, very common meaning: of now, modern (contemporary art, contemporary music). Contemporaneous does not mean modern. It only means in the same period — and that period is often in the past.

Though actually不過其實 it is not the same as contemporary它跟 contemporary 不一樣。Contemporary is the common word contemporary 是比較常用的字, and it has a second, very common meaning而且它還有第二個很常見的意思: of now, modern (contemporary art, contemporary music)就是「現代的」（像 contemporary art、contemporary music）。Contemporaneous does not mean modern contemporaneous 不是「現代的」意思。It only means in the same period它只是指「在同一個時期」 — and that period is often in the past而那個時期通常是在過去。

Writers pick it when they want to stay exact. You will meet it in history books, law, and serious essays, almost never in casual talk.

Writers pick it when they want to stay exact作家想講得精確時會選用這個字。You will meet it in history books, law, and serious essays你會在歷史書、法律文件和嚴肅的論文裡遇到它, almost never in casual talk但幾乎不會出現在輕鬆的對話裡。