monitor  
 noun [ C ] uk/ˈmɒn.ɪ.tər/ us/ˈmɑː.nə.t̬ɚ/
  (PERSON WHO WATCHES)      
 B2 监督员,核查员
a person who has the job of watching or noticing particular things
  United Nations monitors were not allowed to enter the area. 联合国核查员未被允许进入这一地区。 
 - More examples
 - Rosie was chosen to be monitor in class that day.
 - They are employed as monitors to make sure that the organization works within the law.
 - International monitors are keeping watch on the election process.
 
  (TESTING MACHINE)      
  监控器,监测器
a machine that regularly tests something
  a radiation monitor 辐射监测器 
   (SCREEN)      
 B2 显示器,屏幕
a computer screen or a device with a screen on which words or pictures can be shown
  a computer monitor 计算机显示器 
 a TV monitor 电视屏幕 
 Doctors watched the old man's heartbeat on a monitor. 医生们通过显示器监测这个老人的心跳。 
   (AT SCHOOL)      
  (学校的)班长,年级长,教务助理生
a child in school who has special jobs to do
  the library monitor 图书馆助理生 
   (REPTILE)     
 巨蜥(同monitor lizard)
a  monitor lizard 
 monitor       
verb [ T ] uk/ˈmɒn.ɪ.tər/ us/ˈmɑː.nə.t̬ɚ/
C1 监控;监测;监视,密切注视
to watch and check a situation carefully for a period of time in order to discover something about it
  The new findings suggest that women ought to monitor their cholesterol levels. 新发现表明女性应当密切关注她们的胆固醇水平。 
 The CIA were monitoring (= secretly listening to) his phone calls. 中央情报局正在对他的电话进行监听。 
 - More examples
 - A 1200-strong military force will be on hand to monitor the ceasefire.
 - We need to monitor the transaction of smaller deals.
 - They'll use ultrasound to monitor her ovaries to see if they're responding to the treatment.
 - The babies in this unit have various devices attached to them that monitor the vital signs.