n.

1. 简单，简易；简明[U]
   The advantage of the idea was its simplicity.

   这个主意的优点就在于它简单明了。

2. 简明易懂的事物[P]
3. 简朴，朴素[U]
   She dressed with elegant simplicity.

   她的穿着朴素而雅致。

4. 纯朴，单纯[U]
5. 真诚，坦率[U]
6. 无知，愚蠢[U]
   His simplicity made him easily fooled.

   他的无知使他很容易受骗上当。

n.

1. the quality or condition of being simple.
2. a thing that is simple.