Instantaneous means happening at once — no wait you can notice. In careful and scientific English, an instantaneous change is one that takes, for practical purposes, no time. You will hear instantaneous reaction, instantaneous communication, instantaneous death in news and textbooks.

Instantaneous means happening at onceinstantaneous指的是立刻發生 — no wait you can notice沒有任何你能察覺得到的等待. In careful and scientific English在講究精確或科學的英文裡, an instantaneous change一個instantaneous的變化 is one that takes, for practical purposes, no time實際上等於不花時間. You will hear你會聽到 instantaneous reaction instantaneous reaction, instantaneous communication instantaneous communication, instantaneous death instantaneous death in news and textbooks在新聞和教科書裡.

Though actually, in ordinary talk people just say instant or immediate, and they are close. Instantaneous is a little stiffer, and scientists sometimes use it in a strict way: not ‘very fast’, but ‘at this exact instant’. Physicists talk about instantaneous speed — your speed at one pinpoint in time, not over a journey.

Though actually不過實際上, in ordinary talk在日常說話裡, people just say instant or immediate人們就只說instant或immediate, and they are close而這兩個字意思很接近. Instantaneous is a little stifferinstantaneous語感更生硬一點, and scientists sometimes use it in a strict way科學家有時候會很嚴格地使用它: not 'very fast'不是指『很快』, but 'at this exact instant'而是指『就在這一瞬間』. Physicists talk about instantaneous speed物理學家會講instantaneous speed（瞬時速度） — your speed at one pinpoint in time也就是你在某一個時間點上的速度, not over a journey而不是整段行程的速度.

So the tidy dictionary says ‘immediately’, and that is fair, but the word often carries a lab-coat or news-anchor feel.

So the tidy dictionary says 'immediately'所以字典裡工整的解釋會說是『immediately』, and that is fair這樣說沒錯, but the word often carries a lab-coat or news-anchor feel但這個字常常帶著一種實驗室或新聞主播的味道.