furtive, sneak, sneaky, stealthy, surreptitious -- (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")
clandestine, cloak-and-dagger, hole-and-corner, hugger-mugger, hush-hush, secret, surreptitious, undercover, underground -- (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")
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