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" clandestinecloak-and-daggerhole-and-cornerhugger-muggerhush-hushsecretsurreptitiousundercoverunderground
marked by quiet and caution and secrecy; taking pains to avoid being observed "a furtive manner"; "a sneak attack"; "stealthy footsteps"; "a surreptitious glance at his watch" furtivesneaksneakystealthysurreptitious