"离开" 在英语中可以用 "leave" 来表示。这个词是源自中世纪拉丁语 "repnquere"，意思是 "放弃，放下"。例如：

I'm going to leave now. (我现在要离开了。)
He left the office early today. (他今天早早离开了办公室。)

"告别" 在英语中可以用 "say goodbye" 或者 "bid farewell" 来表示。这两个词都源自中世纪英语，"say goodbye" 的意思是 "说再见"，"bid farewell" 的意思是 "告别，辞别"。例如：

She said goodbye to her friends before leaving for the airport. (她在动身去机场之前向朋友们告别。)
He bid farewell to his colleagues before starting his new job. (他在开始新工作之前向同事们告别。)