1. 简单;容易;简明
    The simplicity of something is the fact that it is not complicated and can be understood or done easily.

    e.g. The apparent simplicity of his plot is deceptive...
           他的故事情节貌似简单，其实不然。
    e.g. Because of its simplicity, this test could be carried out easily by a family doctor.
           这种检查非常简单，家庭医生就可以轻松完成。

2. 简单;质朴;朴素
    When you talk about something's simplicity, you approve of it because it has no unnecessary parts or complicated details.

    e.g. ...fussy details that ruin the simplicity of the design...
           破坏了这款设计简洁风格的过多的细节
    e.g. A pair of jewelled earrings will liven up this dress without detracting from its simplicity.
           一对宝石耳环会让这件礼服更出彩而又不失简洁。

3. 非常简单;非常容易
    If you say that something is simplicity itself, you are emphasizing that it is very simple or easy.

simplicity

    e.g. The kitchen is simplicity itself, relying on a combination of good design, craftsmanship and quality materials for its effect...
           厨房非常简洁，这有赖于好的设计、工艺及可体现这种效果的上乘材料。
    e.g. Using a credit card to pay for an order is simplicity itself.
           用信用卡支付订单再简单不过了。