conducted with or marked by hidden aims or methods
- clandestine intelligence operations
- cloak-and-dagger activities behind enemy lines
- hole-and-corner intrigue
- secret missions
- a secret agent
- secret sales of arms
- surreptitious mobilization of troops
- an undercover investigation
- underground resistance
Synonym: clandestinecloak-and-daggerhole-and-corner(a)hugger-muggersecretsurreptitiousundercoverunderground