"立刻"用英语可以说成"immediately"。
"immediately" 是英语中一个副词，意思是"立刻，马上"。它来自拉丁语"immediatus"，意思是"没有任何间隔"。
例句：
Please let me know immediately if there are any changes. (请立刻告诉我如果有任何变化)
The doctor instructed me to take the medicine immediately after meals. (医生告诉我饭后立刻服药)
They left immediately after the meeting. (会议结束后他们立刻离开)