1. (

• 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" ;