undercover

adj.

暗中进行的，秘密的；秘密从事的；私下的，隐蔽的；从事间谍活动的

n.

卧底；

undercover agent卧底；警方密探

1. She worked as an undercover agent for the police.
   她为警察当密探。
2. The undercover payments were discovered.
   那些秘密支付的款项被发现了。

Undercover:Police Surveillance in America
Undercover: Police Surveillance in America
Undercover:authentication usable in front of prying eyes
Mitochondrial proteomics. Undercover in the lipid bilayer
Parts unknown: Undercover ethnography of the organs-trafficking underworld
Becoming an Undercover Police Officer: A Note on Fairness Perceptions, Behavior, and Attitudes
Undercover careseekers: simulated clients in the study of health provider behavior in developing countries.
Molecular Shuttles Operating Undercover:  A New Photolithographic Approach for the Fabrication of Structured Surfaces Supporting Di...
The Depravity of "Torchbearer"——Another Interpretation of The Undercover and a Deliberation with Mr.Mu Gong
Fasteners for clamping sheet-form members, and apparatus and method using such fasteners to attach undercover onto underside of vehi...