顿时的英文：
at once
immediately
forthwith

参考例句：

My scalp began to prickle as I realized the horrible truth.
我了解到了那令人恐惧的事实,顿时感到不寒而栗.

The fire flared up as I put more logs on it.
我加上了几块木柴,火顿时旺起来.

He had been instantly shocked by the fragility of his opponent and the ease of his advantage.
他发现对方软弱得毫无抵抗力，自己不费吹灰之力占了上风，顿时大吃一惊。

Immediately a funeral gloom settled like a noonday darkness upon the city
顿时，全城天昏地暗，一片哀伤。

Cut off all hopes of reconciliation
使一切和解的希望顿时告吹

The quiet village suddenly became astir
寂静的山村，顿时沸腾起来。

At once a draft of cool fresh air suffused the room.
顿时一阵凉快新鲜的微风吹遍了房间。

A blush mantled over the bronzed cheek of the gladiator
斗士古铜色的脸膛顿时涨得通红。

The meeting hall was seething at once
会场上顿时沸腾起来了。

The news threw the family into a panic.
这个消息使那一家人顿时陷入惊恐不安。

once是什么意思：
adv. 一次，一回；一度；曾经
conj. 一旦；一…就…
n. 一次；一回

Once is no custom
一次不成例

Do it for this once.
就干这一次吧。

Gordon is at once modest and clever.(at once …and…既..又)
戈登既聪明又谦逊

immediately是什么意思：
adv. 立即；直接地
conj. 一…就

immediate bridge
立即齿桥

The law is effective immediately.
这项法律立即生效。

The evidence has no immediate bearing on the case.
该证据与本案无直接关系。

forthwith是什么意思：
adv. 立即；毫不犹豫地

I could have you arrested forthwith!
我可以立即逮捕你！

A lane was forthwith opened through the crowd of spectators.
围观的人群中挤开了一条通路。

And they forthwith left their nets and father, and followed him.
他们也立刻舍下鱼船和自己的父亲，跟随了他。