discretion  
noun [ U ] uk/dɪˈskreʃ.ən/ us/dɪˈskreʃ.ən/
  (CAREFUL BEHAVIOUR)      
 C2 慎重,谨慎;守口如瓶
the ability to behave without causing embarrassment or attracting too much attention, especially by keeping information secret
  "Can you trust him with this?" "Yes, he's the soul of discretion (= he will not tell other people)." “在这件事上你能相信他吗?”“当然,他可是个守口如瓶的人。” 
   (RIGHT TO CHOOSE)      
 formal决定权;决策力 
the right or ability to decide something
  Students can be expelled at the discretion of the principal (= if the principal decides it). 校长有权开除学生。 
 I leave the decision to your discretion (= for you to decide). 我让你来决定这件事。 
 Idiom  
discretion is the better part of valouridiom  saying 勇敢者贵在审慎。
said when you believe it is wise to be careful and avoid unnecessary risks