clandestine

他们在进行秘密会谈，商讨合作计划。

They held a ___clandestine meeting to discuss the cooperation plan.

他们私下交换文件的方式很隐蔽。

Their ___clandestine way of exchanging documents was very discreet.

特工们在公园长椅下交换了秘密文件。

The agents made a ___clandestine exchange of documents under a park bench.