simplicity  
noun [ U ] uk/sɪmˈplɪs.ə.ti/ us/sɪmˈplɪs.ə.t̬i/
  (EASY)      
 C1 简单,简易
the fact that something is easy to understand or do
  The advantage of the plan is its simplicity. 这项计划的优点是简单易行。 
 The test was simplicity itself (= very easy). 考试非常简单。 
 - More examples
 - I prefer the second option - its advantages are simplicity and cheapness.
 - All the ideas have a stunning simplicity.
 
  (NATURAL)      
  天真;纯朴
the fact that something is ordinary, traditional, or natural, and not complicated
  The old people led a life of great simplicity (= with few possessions and little money). 这位老人过着十分简朴的生活。 
   (PLAIN)     
 朴素,简朴
the fact that something is plain and has no decoration