plain用作名词意思是“平原”,指起伏极小,海拔较低的广大平地,常用作复数形式。

Is the coastal plain good for growing crops?沿海的平原适合种庄稼吗?
I was fearful lest we should strike the timbered edge of the plain.我害怕我们会进入这个平原边缘的林带。
The wind whistled across the plain.风呼呼地吹过旷野。
Animals range over the hills and plains.动物在山丘和平原上出没。
He ranged the plains.他在平原上走来走去。
The vast plains of this country spread for hundreds of miles.这个国家辽阔的平原绵延数百英里。
Most of the ocean bottom is made up of smooth plains.海底大部分是由平坦的平原构成。
China's vast plains are distributed mainly in the eastern part of the country along the seacoast.中国的大平原主要分布在东部沿海地区。
South of the Great Wall, boundless plains stretch far out of sight.长城南面是一望无际的平原。
They turned the hills into orchards and plains into granaries.他们把山坡变成了果园,把平地变成了粮仓。

［同义词］ adj.  clear, obvious, visible, simple, frank n.  plateau, prairie
［反义词］ adj.  indistinct, vague, difficult, indirect
［词源］  ＜拉丁语planus(平坦,清楚,简单)

1.plain作形容词的基本意思是“清晰的,明白的”,指能被人清楚地看到或听到。plain作“朴素的,简单的,平常的”解时,可指衣着朴素,缺乏装饰; 也可指人的相貌平常,没有特别引人注目之处。plain作“坦白的,坦率的,真诚的”解时,一般指人的行为和思想。plain作以上解释时在句中可用作定语或表语。
2.plain还可作“完全的,十足的,彻底的”解,在句中只用作定语,无比较级和最高级形式。
3.当plain的主语是动词不定式或that从句时,常用于形式主语结构。

as plain as the nose on one's face
显而易见 very obvious
Surely you can see what's wrong; it's as plain as the nose on your face.当然你能知道出了什么差错,这显而易见。
It's as plain as the nose on your face.If we haven't got any money, we can't buy a television.如果我们没有钱,就不能买电视机,这是明摆着的事。

in plain English
用直率的或简单明了的英语,不拐弯抹角而直说 bluntly or simply expressed
Please rephrase the question in plain English.请用明白的英语重新提出问题。
The book is written in plain English.那本书是用简明英语写的。
If you want me to go, why didn't you say so in plain English instead of making vague hints?你想叫我走,为什么拐弯抹角而不直说?


in plain sight
一目了然 be clear at a glance
She counted more than a dozen in plain sight as the steamer drew closer.当轮船靠近时,她一眼就数出了十多艘来。

plain sailing
十分顺利; 一帆风顺 course of action that is simple and free from trouble
The drive is plain sailing once you get out of the suburbs.出了郊区,车就容易驾驶了。
After we engaged a guide, everything was plain sailing.我们请了向导后,一切都顺利了。


plain speaking
诚实〔坦率〕地说 honest〔open〕 talk
They are all so suspicious of each other; a little plain speaking would do a lot of good.他们都是相互猜疑,如果稍微诚实坦率些,那就会好多了。

用作定语
▲～+n.
The plain truth is that she will never return.事实很明显,她永远不会回来了。
The plain fact is that we just can't afford it.明显的事实是我们买不起它。
He refused to commit himself to a plain “yes” or “no”.他拒绝明确答复行还是不行。
She's in plain clothes.她的穿着很朴素。
He wore a plain cotton uniform.他穿着一身朴素的棉制服。
We are leading a plain life.我们过着朴素的生活。
Comrades must be helped to preserve the style of plain living and hard struggle.务必使同志们保持艰苦奋斗的作风。
The girl has a good figure but a plain face.那个女孩子体形很美,但长相一般。
From a rather plain child she had grown into a beautiful woman.她从一个相貌平平的孩子长成了一个美丽的女子。
I'm afraid she's rather a plain girl.恐怕她是一个相貌相当普通的姑娘。
I'll tell you everything in plain words.我将坦白地把一切事情告诉你。
The teacher gave me a plain talk about my mistakes.老师就我的错误和我进行了坦率的交谈。
He is fond of plain dealing and plain speaking.他喜欢办事光明磊落,说话直言不讳。
He's plain stupid.他是个十足的笨蛋。
It's just plain foolishness to spend all your pay as soon as you get it!你的工资一到手就花光,真是愚不可及!
用作表语
▲S+be+～
The meaning of the sentence is quite plain.这个句子的意思相当清楚。
The figures in the picture are quite plain.照片上的人像很清楚。
Whatever the terms used, the facts are plain enough.不管怎么说,事实再清楚不过了。
I should think that her motive is quite plain.我应该想到她的动机是十分清楚的。
His guilt is plain because the stolen money was found in his briefcase.他的罪行已清楚了,因为失窃的钱是在他的皮包里发现的。
Her dress is severely plain.她的服装很朴素。
▲S+be+～+prep.-phrase
I will be plain with you and tell you the truth.我跟你开门见山地说实话。
He was quite plain about his feeling on the matter.他毫不掩饰他对那件事的感情。
▲It is/was+～+to-v
It's plain to see you haven't done this before.显然你以前没做过这种事情。
▲It is/was+～+that-clause
It's quite plain that you haven't been paying attention.你显然一直都没好好地留意。
It is quite plain that he is mistaken.显然是他错了。
用作宾语补足语
▲S+V+O+～
I hope I've made myself plain on this issue.我希望我已把这个问题说清楚了。
There is no more money—do I make myself plain?现在也没钱了——我的意思清楚吗?
He made it plain to us that he did not wish to continue.他向我们明白地表示他不想继续做下去。

plain, ugly
参见ugly条。