top secret
adjective uk/ˌtɒp ˈsiː.krət/ us/ˌtɑːp ˈsiː.krət/
（情报）绝密的
(of information) extremely secret and not to be told to anyone outside a particular group of people
These papers are top secret. 这些文件是绝密的。
[ before noun ] a top-secret military research project 绝密的军事研究项目