英汉词典

1. 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.

    e.g. 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。
    e.g. He placed the paper in a plain envelope...
           他把论文装进一个空白信封里。

2. 朴素的；简朴的
    Something that is plain is very simple in style.

    e.g. 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。
    e.g. 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。