1.sudden的意思是“突然的,忽然的,迅速而意外的”,指事先没有预料到事情会发生,所以当事情发生时使人感到很意外。
2.all of a sudden的意思是“突然地,出乎意料地”,常用于口语中。也常用on a sudden,意思与all of a sudden相同,但不如all of a sudden正式或常见。

all of a sudden〔on a sudden〕
突然地,突如其来地,猛然地 suddenly
He was writing his essay when, all of a sudden, he was seized with giddiness.他正在写论文,突然一阵头晕。
I was sitting quietly reading when all of a sudden a stone came hurling through the window.我正安安静静地坐着看书,突然从窗外飞来一块石头。
Life seemed on a sudden empty and meaningless.生活似乎突然显得空洞而无聊。
The driver has swerved on a sudden to avoid a file of geese.为了躲避一队鹅,司机突然来个急转弯。

用作定语
▲～+n.
We were struck dumb by her sudden outburst of anger.她突然大发脾气,弄得我们都哑然失色。
The sudden arrival of guests forced her to change her plans.客人们的突然到来迫使她改变了计划。
He made a sudden stop.他突然停了下来。
He requested their sudden help.他要求他们迅速帮助。
Our clothes were saturated with the sudden heavy rain.突降的大雨淋湿了我们的衣服。
We scrambled for cover against the sudden rain.我们当时都争先恐后地找地方躲避那场急雨。
A sudden wind swept a pile of leaves in.突然吹起一阵风,刮进一堆树叶来。
The birds were scared by the sudden barking of a dog.鸟被突然的狗叫声吓跑了。
We were shattered to hear of her sudden death.听到她突然死了,我们都感到震惊。
Her sudden death upset everybody.她的突然死亡令人人心烦意乱。
He felt a sudden sharp pain in his heart.他突然感到心里一阵剧痛。
He was seized with sudden chest pains.他突然感到胸部疼痛。
He was seized with a sudden desire to leave the place.他突然想离开这地方。
She was seized with a sudden desire to laugh, at a most unsuitable moment in the performance.在演出中最不该笑的时候,她突然想笑。
用作表语
▲S+be+～
Your marriage was sudden.Have you thought things over properly?你结婚太突然了,都考虑好了吗?
This marriage is very sudden—they've only known each other a few weeks.这桩婚事来得非常突然——他们才认识了几个星期。
▲S+be+～+in sth/v-ing
He was sudden in his actions.他行动迅速。
The boy is sudden in eating.这个男孩吃饭很快。

sudden, fast, hasty, quick, rapid, swift
参见fast条。

［同义词］   abrupt, swift, unexpected, unforeseen
［反义词］   slow
［词源］  ＜中古法语sodain＜拉丁语subitus (突然的)