clandestine
adjective formal uk/klænˈdes.tɪn/ us/klænˈdes.tɪn/
（尤指从事不被官方允许的活动）秘密的，暗中的，私下的
planned or done in secret, especially describing something that is not officially allowed
The group held weekly clandestine meetings in a church. 这个团体每星期都在教堂举行秘密集会。
He has been having a clandestine affair with his secretary for three years. 他和秘书私通已有3年了。
She undertook several clandestine operations for the CIA. 她执行过中央情报局的好几次秘密行动。
Synonyms: cloak-and-daggerhush-hush secret surreptitiousundercover underground