"立即"的英文表达是"immediately"。这个词来源于拉丁文"medius"和"mediately"，意思是"in the middle"或"in between"。"Immediately"是"mediately"的变形，意思是"without any delay"。
下面是一些英文例句及其中文翻译：
Please respond to this email immediately. 请立即回复这封邮件。
The fire department arrived on the scene immediately. 消防队立即赶到现场。
The doctor told me to stop taking the medication immediately. 医生告诉我立即停止服用药物。