1. (

• 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" ;

2. (

• 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" ;