undercover agent 卧底人员
undercover operation 秘密行动
go undercover 秘密潜入
A: Did you know the detective is working undercover?
A：你知道那名侦探正在秘密执行任务吗？
B: No, I thought he was in the office.
B：不知道，我以为他在办公室里。
1) 秘密的
2) 卧底的
3) 隐蔽的
1. 秘密的；卧底的
adjective/adverb
1. working in secret, especially to investigate something.
Synonym: secret, covert