单色的；素色的；无花纹（或图案、字迹）的

A plain object, surface, or fabric is entirely in one colour and has no pattern, design, or writing on it.

1. In general, a plain carpet makes a room look bigger...

   一般来说，单色的地毯使房间显得更宽敞。

2. He placed the paper in a plain envelope...

   他把论文装进一个空白信封里。

3. He wore a plain blue shirt, open at the collar.

   他穿一件素净的蓝色衬衫，领口敞着。

朴素的；简朴的

Something that is plain is very simple in style.

1. Bronwen's dress was plain but it hung well on her...

   布朗温的长裙虽然朴素，却很合身。

2. It was a plain, grey stone house, distinguished mainly by its largely unspoilt simplicity.

   这是一幢简朴的灰石房子，主要以其天然简约的风格显得与众不同。

明显的；明白的；清楚的

If a fact, situation, or statement is plain, it is easy to recognize or understand.

1. It was plain to him that I was having a nervous breakdown...

   他能明显地看出我快要精神崩溃了。

2. He's made it plain that he loves the game and wants to be involved still.

   他明确表示自己热爱这项运动，并仍想参与其中。

（相貌）平常的，不好看的

If you describe someone as plain, you think they look ordinary and not at all beautiful.

1. ...a shy, rather plain girl with a pale complexion.

   肤色苍白、相貌平平的害羞女孩

平原；（几乎没有树木的）大片平地

A plain is a large flat area of land with very few trees on it.

1. Once there were 70 million buffalo on the plains.

   北美大平原上曾有过7,000万头野牛。

（用于形容词前加强语气）显然，完全地

You can use plain before an adjective in order to emphasize it.

1. The food was just plain terrible.

   这食物实在太难吃了。

（尤在与另一个更加不同寻常或让人印象深刻的名字比较时表示强调）普通的，平凡的

You can use plain before a name to emphasize how simple and ordinary it is, especially when you are comparing it with another more unusual or impressive name.

1. Why couldn't they call you plain Ann or Alice like the rest?

   他们为什么不能像其他人一样，给你取个普普通通的安或艾丽斯的名字呢？

（警察）穿便衣的

If a police officer is in plain clothes, he or she is wearing ordinary clothes instead of a police uniform.

1. Three officers in plain clothes told me to get out of the car.

   3名便衣警察让我下车。