- Involving secret work within a community or organization, especially for the purposes of police investigation or espionage: an undercover police operation [as adverb]: he worked undercover in Northern IrelandMore example sentences
covert, secret, clandestine, private, confidential, conspiratorial, underground, surreptitious, furtive, cloak-and-dagger, hole-and-corner, hugger-mugger, back-alley, backstair, stealthy, closet; intelligence; hidden, concealed, masked, veiled, shrouded; Military black• informal hush-hush, sneaky
- In March 1999, police began an undercover surveillance operation on the prison officer.
- Two cases emphasise the need for the use of cautions in connection with police undercover operations.
- The charges arise out of a police undercover operation in the latter part of 1998.